Rhamnolipids: Production, Performance, and Application

  • Till Tiso
  • Stephan Thies
  • Michaela Müller
  • Lora Tsvetanova
  • Laura Carraresi
  • Stefanie Bröring
  • Karl-Erich Jaeger
  • Lars Mathias BlankEmail author
Living reference work entry
Part of the Handbook of Hydrocarbon and Lipid Microbiology book series (HHLM)


A circular bioeconomy requires the use of renewable resources to produce high-value specialty chemicals or pharmaceuticals, and also fine and bulk chemicals. Here, the surfactant market represents an ideal test case, because surfactants can cover diverse product classes ranging from fine to bulk chemicals and thus including large differences in purity and price. Biosurfactants produced by microbes from renewable resources are discussed for decades, and recently, sophorolipids arrived in the market, produced by fermentation of high-performing production strains and combined with simple product purification thus reaching low product prices.

Here, we review the current status of rhamnolipid research and applications. Molecular diversity of rhamnolipids and biochemical pathways involved in their synthesis are presented, and physicochemical parameters governing emulsification, foaming, and other properties of rhamnolipids are summarized, followed by applications in many different industries including the agro and pharma industry. We finish with a patent survey that covers rhamnolipid production and potential applications of these biosurfactants. We also tried to identify knowledge gaps that might limit a more rapid establishment of rhamnolipids in the markets.


Hydroxy Fatty Acid Emulsification Activity Patent Family Rhamnolipid Production Oily Sludge 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

1 Introduction

Bioeconomy requires to establish novel value chains to valorize waste streams to products for the chemical industry . The concept of biorefinery attempts to integrate biomass and waste conversion and the production of fuels, power, heat, and value-added chemicals. For the realization of a bio-based economy, biorefinery requires industrial scale production of bulk products for scale and high-value products for margin.

Microbial lipids, e.g., neutral lipids from oleaginous yeast, are discussed as alternative to plant-derived oils for the synthesis of biodiesel. While liquid fuels are by far the largest chemical products volume wise, easily guaranteeing large scales in a biorefinery, the contributions of microbial lipids are still under debate. Alternatively, biosurfactants represent an exceptional class of microbially produced lipids, which comprise surface active compounds produced by different fungal and bacterial microorganisms (Lang and Trowitzsch-Kienast 2002; Rosenberg and Ron 2013). This group includes secreted secondary metabolites of diverse composition and from different biosynthetic pathways ranging from small molecules like glycolipids, lipopeptides, and acylated amino acids to polymeric high molecular weight compounds (Smyth et al. 2010; Soberón-Chávez and Maier 2011; Thies et al. 2016). Beyond surface activity, biosurfactants often show beneficial properties like biodegradability, low toxicity (Johann et al. 2016), ability for metal ion complexation as well as antibacterial and antifungal effects (Banat et al. 2000; Marchant and Banat 2012a). In addition, the resource-efficient production from renewable resources is generally listed as benefit of biosurfactants.

Notably, some of these properties are reiterated by many authors, while experimental evidence is often scarce. This might be due to the large range of molecular structures that not only exists between the different classes but also in defined classes of biosurfactants. For example, rhamnolipids differ in the number of hydroxy fatty acid and rhamnose residues, in which the hydroxy fatty acids differ in length, and were even reported with additional decorations including methylation and acetylation (see Abdel-Mawgoud et al. (2010) for details). Consequently, analytical challenges result, which at least partly explain the low comparability of published studies.

While high biodegradability (low environmental accumulation) can be assumed for the structures including ester and glycosidic bonds, other properties like low toxicity and resource-efficient production seem more anecdotal than supported by detailed studies.

2 Rhamnolipids

2.1 Congeners and Biosynthesis

Rhamnolipids are currently considered the best-studied representatives of bacterial biosurfactants (Müller et al. 2012). Due to excellent surfactant properties, low toxicity, high biodegradability, and antimicrobial effects, rhamnolipids are discussed for various applications (section “Applications of Rhamnolipids”), e.g., in cleaning agents, cosmetics, food industry, biocontrol, and soil remediation (Fracchia et al. 2014). A blueprint rhamnolipid consists of a hydrophobic domain with generally two molecules of hydroxy fatty acids forming a 3-(hydroxyalkanoyloxy)alkanoic acid (HAA), which is connected via a glycosidic bond to a hydrophilic part comprising one or two molecules of the sugar rhamnose, thus forming mono-rhamnolipids and di-rhamnolipids, respectively (Jarvis and Johnson 1949; Ito et al. 1971). Many different variations of both commonly anionic glycolipids were described (Fig. 1a), most of them varying in the incorporated β-hydroxy fatty acids with respect to chain length and degree of saturation. An excellent overview on the congener diversit y is given by Abdel-Mawgoud et al. (2010). The reported lengths range between chains of 6 and 16 carbon atoms and 24 carbon atoms in a recent single report, with saturated chains dominating, but also occurring of chains with one or rarely two double bonds (Abdel-Mawgoud et al. 2010; Nie et al. 2010; Jadhav et al. 2011). Besides that, there are also congeners described, which occur in smaller amounts and deviate from the blueprint in their degree of acylation. They contain only one β-hydroxy fatty acid, here again a certain range of chains is possible (Lang and Trowitzsch-Kienast 2002), or, reported in a limited number of studies, even three chains or a further acylation/methylation (Hirayama and Kato 1982; Andrä et al. 2006; Abdel-Mawgoud et al. 2010). Natural rhamnolipid producers usually secrete a cocktail of different congeners with at least showing a certain range of fatty acids, as it is also common for other acylated metabolites (Youssef et al. 2005; Dwivedi et al. 2008; Thies et al. 2014). The production of mono- and di-rhamnolipid mixtures is also frequently observed.
Fig. 1

Congeners and biosynthesis of rhamnolipids. (a) Molecular variations of rhamnolipids. Depicted is a typical di-rhamnolipid scaffold, and variable components are indicated. (b) Schematic illustration of rhamnolipid biosynthesis from primary metabolism-derived precursor molecules. Genetic organization of rhlA, B, C, and the architecture of the central carbon metabolism vary between different producer strains

At least two enzymes are required for the biosynthesis of rhamnolipids from the precursor metabolites dTDP-rhamnose and activated β-hydroxy fatty acids (Fig. 1b): (i) the acyltransferase RhlA for the generation of HAA and (ii) the glycosyltransferase RhlB for glycosidic bond formation (Abdel-Mawgoud et al. 2011). For a long time, it was assumed that these two proteins have to form a dimer to catalyze rhamnolipid synthesis: hence, they are often designated as subunit A and B of a rhamnosyltransferase, which is challenged by a very recent study that indicates an independent mode of action of both enzymes in vivo (Wittgens et al. 2017). For synthesis of di-rhamnolipids, a second molecule of activated rhamnose is added to mono-rhamnolipids by the rhamnosyltransferase RhlC (Burger et al. 1966). Further enzymes that may be involved in the biosynthesis of additional acylated variants or in the formation of monoacylated rhamnolipids were not elucidated until today. Regarding the latter variants, at least hints are reported that synthesis is rather obtained by the degradation of common rhamnolipid species due to HAA ester cleavage than by promiscuity of RhlB (Wittgens et al. 2017). Likewise unsolved is the mode of secretion of the intracellular biosynthesized molecules into the environment.

Both precursor molecules are supplied by the primary metabolism of the cells. dTDP-rhamnose, which is very common in Gram-negative bacteria, e.g., for the formation of LPS, is derived from glucose-6-phosphate within the sugar metabolism from. β-Hydroxy fatty acids in activated forms are part of the general fatty acid-related metabolic pathways, in de novo synthesis as well as β-oxidation. The stereochemistry of the HAA fatty acids (R-3-hydroxy-acyls (Schenk et al. 1997; Bauer et al. 2006)) resembles the conformation of intermediates of de novo synthesis (FAS II). On the other hand, there are studies, which show a direct influence of β-oxidation to rhamnolipid biosynthesis. Currently proposed is a contribution of both pathways to the R-3-hydroxy-fatty acid pool available for rhamnolipid biosynthesis by interlinks between degradation and synthesis pathways and by R-specific enoyl-CoA hydratases, which branch off intermediates from β-oxidation and convert them to the correct stereoisomer for HAA biosynthesis (Abdel-Mawgoud et al. 2014; Dobler et al. 2015).

2.2 Producer Strains

Microbial rhamnolipid production was initially discovered within the opportunistic human pathogen Pseudomonas aeruginosa (Jarvis and Johnson 1949), which is still the best characterized and most frequently applied organism for rhamnolipid production (Müller et al. 2010; Müller et al. 2012). Meanwhile, many more producers were discovered, several of them belonging to the Pseudomonadales with Pseudomonas sp. (like particular strains of P. chlororaphis, P. fluorescens, P. putida, P. stutzeri) or Acinetobacter calcoaceticus (Abdel-Mawgoud et al. 2010). Also other members of γ-proteobacteria are reported to produce rhamnolipids like Pantoea ananatis (Smith et al. 2016) and other Pantoea strains, Enterobacter sp. (Rooney et al. 2009; Hošková et al. 2013), Thermus sp. (Rezanka et al. 2011), and certain Serratia rubidaea strains (Nalini and Parthasarathi 2014). Still another genus with an apparently widespread distribution of rhamnolipid biosynthesis pathways is Burkholderia sp. (β-proteobacteria) with many strains capable of the production of rhamnolipids, e.g., B. plantarii, B. thailandensis, and B. glumae (Costa et al. 2011; Tavares et al. 2013; Funston et al. 2016; Elshikh et al. 2017). Remarkably, rhamnolipid synthesis was also discovered within members of completely different prokaryotes, namely, members of Actinobacteria (Kügler et al. 2015) and other Gram-positive bacteria (Lee et al. 2005).

The genetic organization of biosynthetic genes varies within rhamnolipid producers. In P. aeruginosa, they are split into two bicistronic operons, namely, rhlAB and rhlC together with a putative membrane protein of so far unknown function. In B. glumae, these four genes are clustered in one operon. Additionally, B. thailandensis and B. pseudomallei are reported to contain two copies of rhl operons within the genome, which both contribute to biosynthesis (Dubeau et al. 2009). BLAST analysis (Zhang et al. 2000) of published Burkholderia sp. genomes indicates that this is not uncommon amid this phylum as it predicts B. cepacia, B. cenocepacia, B. ubonensis, and B. metallica to have likewise two rhl clusters. Nonetheless, other strains of Burkholderia, e.g., B. glumae, harbor only one copy (Voget et al. 2015).

Furthermore, strains exist, which harbor only rhlA and rhlB and consequently produce exclusively mono-rhamnolipids, like P. chlororaphis (Gunther et al. 2005).

Natural biosynthesis is usually controlled by a complex network of regulatory pathways as is common for secondary metabolite production, with quorum sensing systems as a central component. A comprehensive description of the complex regulation of rhamnolipid biosynthesis in P. aeruginosa was recently published (Lovaglio et al. 2015).

Many different natural functions of rhamnolipids are proposed including solubilization and uptake of hydrophobic substances, improving surface motility, fighting competitors and predators, or contributing to virulence, and important roles during biofilm formation as summarized by Abdel-Mawgoud et al. (Abdel-Mawgoud et al. 2010).

2.3 Production Strategies

Due to their physical and chemical properties, rhamnolipids are of interest for a variety of biotechnological applications. Consequently, many studies were conducted to develop processes for biotechnological rhamnolipid production and to improve the biosurfactant yields. Despite its pathogenicity, many studies focused on P. aeruginosa reporting batch, fed-batch or resting cell process strategies with different carbon sources. Hence, P. aeruginosa is currently still the most advanced production strain for mid- and large-scale rhamnolipid production (Müller et al. 2010; Müller et al. 2012). Best results were obtained with hydrophobic carbon sources like plant oils or alkanes with frequently reported titers at a two-digit g/L scale (Leitermann et al. 2010), exceptionally high titers of up to 112 g/l were reported once in a patent application (Giani et al. 1995).

Nonetheless, in order to circumvent safety and regulation issues due to pathogenicity, several studies were conducted exploring processes with nonpathogenic producer strains, e.g., P. fluorescens and P. chlororaphis (Gunther et al. 2005; Toribio et al. 2011), or strains of P. aeruginosa, Acinetobacter, and Enterobacter claimed to be nonpathogenic (Hošková et al. 2013; Grosso-Becerra et al. 2016). Much attention in this context is furthermore payed to the genus Burkholderia containing many rhamnolipid producers that are non-hazardous for human beings (Hörmann et al. 2010; Toribio et al. 2010; Costa et al. 2011; Díaz De Rienzo et al. 2016; Funston et al. 2016).

A different strategy uses recombinant production strains, thus avoiding safety issues and furthermore circumventing complex metabolic regulation systems as depicted in Fig. 2. Typical P. aeruginosa fed-batch fermentations reveal a strong dependence of rhamnolipid production on the growth (Fig. 2a, b). After entering the stationary phase, the specific rhamnolipid production rate increases, until reaching its maximum and subsequently declines. In contrast, recombinant rhamnolipid synthesis is uncoupled from growth resulting in a constant-specific rhamnolipid production rate (Fig. 2c, d).
Fig. 2

Cultivation strategies using the native rhamnolipid producer P. aeruginosa (left) in comparison to the recombinant cell factory P. putida (right). (a) and (c): courses of CDW, RL, and substrate concentrations. Blue dots show RL titers, while dark yellow rectangles show CDW. Red diamonds represent glucose and dark cyan sunflower oil concentrations. The line show fitted trends. (b) and (d): RL production, growth, and substrate consumption rates during cultivation. The dark yellow solid lines show the growth rates, while the dotted blue lines show RL productivity. The red dashed line represents glucose consumption and the dashed-dotted dark cyan line shows the trend for sunflower oil consumption. The data for the P. aeruginosa cultivation was taken from Müller et al. (2010), while the data for the cultivation of P. putida was taken from Wittgens et al. (2011)

To achieve decoupled production in recombinant strains, the implementation of artificially controlled rhl genes in nonpathogenic natural producers may be one approach to increase their performance and/or modify rhamnolipid composition (Tavares et al. 2013). A more frequently applied strategy generates completely novel artificial production systems, where biosynthesis genes from natural rhamnolipid producers were introduced into suitable nonpathogenic host bacteria that are not capable of rhamnolipid formation by nature resulting in safe production strains with adjustable rhlAB(C) expression characteristics (Table 1). Applying this strategy, mono-rhamnolipid production was achieved by the introduction of P. aeruginosa rhlAB into E. coli, P. fluorescens, P. oleovorans, or P. putida (Ochsner et al. 1995; Kryachko et al. 2013). In particular the latter strain appears to be excellently suited for recombinant rhamnolipid production (Tiso et al. 2014, 2015). Consequently, there are several reports of successful strategies for rhamnolipid production with P. putida, in particular the certified safety strain KT2440 and derivatives thereof, yielding titers at g scale (Fig. 2) (Loeschcke and Thies 2015). Interestingly, introducing the genes from P. aeruginosa yielded the same congener distribution in P. putida (Behrens et al. 2016a, b, c). Different expression systems were evaluated in these studies for the expression of the ca. 2 kb operon, namely, the synthetic hybrid promoter P tac (Ochsner et al. 1995; Wittgens et al. 2011; Setoodeh et al. 2014; Wittgens et al. 2017), completely different synthetic promoters (Blank et al. 2013a; Beuker et al. 2016a, b; Tiso et al. 2016; Wigneswaran et al. 2016), or the native regulation system via coexpression of the cognate autoinducer-dependent transcription factor/autoinducer synthase pair RhlR/RhlI from P. aeruginosa (Cha et al. 2008; Cao et al. 2012). To our knowledge, Beuker et al. (2016b) achieved the highest titer (14.9 g/L) with a recombinant system with a yield (Yrhamnolipid/substrate) of 10 mg/g glucose applying synthetic promoter-controlled expression of rhlAB in P. putida.
Table 1

Summary of approaches for recombinant rhamnolipid production (Updated from Loeschcke and Thies 2015)

Origin of genesa

Expression hostb

Expression strategyc

Max titersd



P. aeruginosa

E. coli

P tac , rhlAB

<0.02 g/L

(Ochsner et al. 1995)

E. coli

Plac, rhlAB

0.005 g/L

(Kryachko et al. 2013)

P. fluorescens

P tac , rhlAB

<0.02 g/L

(Ochsner et al. 1995)

P. oleovorans

P tac , rhlAB

<0.02 g/L

(Ochsner et al. 1995)

Burkholderia kururiensis

P tac , rhlAB

5.67 g/L

(Tavares et al. 2013)

P. putida KT2442

P tac , rhlAB

0.60 g/l

(Ochsner et al. 1995)

P. putida KCTC 1067

Pnative(RhlRI), rhlABRI

7.3 g/l

(Cha et al. 2008)

P. putida KT2440

P tac , rhlAB, dΔphaC1

1.5 g/l

(Wittgens et al. 2011)

P. putida KT2440

Pnative(RhlRI), rhlABRI

1.68 g/l

(Cao et al. 2012)

P. putida KT2440

P tac d/Psynthetic, rhlAB

d ΔphaC 1

up to 12.5 g/l

(Blank et al. 2013a)

P. putida KT2440

P tac , rhlAB

0.57 g/l

(Setoodeh et al. 2014)

P. putida KT2440

Psynthetic, based on PrRNA, rhlAB

0.02 g/l/0.08 g/l in biofilm reactor

(Wigneswaran et al. 2016)

P. putida KT2440

Psynthetic, rhlAB

0.6 g/l

(Beuker et al. 2016a)

P. putida KT24401


Psynthetic, rhlAB

13.2 g/l

(Tiso et al. 2016)

P. putida KT2440

Psynthetic, rhlAB

14.9 g/l

(Beuker et al. 2016b)

+ Di-rhamnolipids

P. aeruginosa

P. chlororaphis


0.1 g/L

(Solaiman et al. 2015)

P. putida KT2440

P. putida GPp104

P lac rhlAB/rhlABM, rhlABC/rhlABMC

di-RL: 0.11 g/l/OD600

(Schaffer et al. 2012)

P. putida KT2440-derived BOA-PP-002

rhaPBAD, rhlABC, d alkBGT from P.putida Gpo1

>1.2 g/l

(Gehring et al. 2016)

P. putida KT2440

P tac , rhlAB/rhlABC/rhlC

0.005 g/l (mono-RL)

0.004 g/L (mixture)

(Wittgens et al. 2016)

B. glumae

P. putida KT2440

P tac , rhlAB(C)

0.08 g/l (mono-RL),

0.05 g/l (mixture)

(Blank et al. 2013a)

Source organisms whose corresponding biosynthetic genes were employed (a) are listed together with the applied production host (b) and the respective expression strategies (c). Here, promoters and genes are named. Additional strain engineering is indexed (d). Product yields are taken from the original publications. (RL rhamnolipid)

Recombinant production of di-rhamnolipids appears to be less pursued; nonetheless, successful studies are also reported. One strategy is the expression of P. aeruginosa rhlC in natural mono-rhamnolipid producers as P. chlororaphis (Solaiman et al. 2015). Other studies describe the heterologous expression of all three rhamnolipid synthesis genes in P. putida. The expression of rhlABC from P. aeruginosa yielded up to 113 mg/l/OD600 using PHA-deficient P. putida GPp104 (Schaffer et al. 2012). Blank et al. (2013a) reported the production of both mono- and di-rhamnolipids expressing rhlAB(C) genes not only from P. aeruginosa but also Burkholderia glumae PG1 controlled by P tac , yielding 80 mg/l of pure mono-rhamnolipids and 50 mg/l of a mixture, respectively. Two strategies to achieve di-rhamnolipid production in P. putida were recently described (Wittgens et al. 2017). Here, biosynthesis was achieved either by the expression of an artificial operon of P. aeruginosa rhlABC or by feeding of mono-rhamnolipids to an rhlC-expressing strain, thereby proving uptake of the glycolipids by P. putida. Gehring et al. reported a strategy for di-rhamnolipids production in advance of an industrial process. They implemented P. aeruginosa like rhlABC genes controlled by a rhamnose inducible promoter in P. putida KT2440 (Gehring et al. 2016).

Metabolic engineering of producer strains in general was identified as useful strategy for process optimization. Hereby, the utilization of more suitable carbon sources can be implemented; moreover the host’s metabolisms can be streamlined toward rhamnolipid production, e.g., by the elimination of competing pathways, boosting the primary metabolism or enhancing (recombinant) biosynthesis gene expression (Wittgens et al. 2011; Martinez-Garcia et al. 2014; Tiso et al. 2016).

3 Physicochemical Characterization of Rhamnolipids

Due to their surface activity, biosurfactants are, like oil-based surfactants, extensively discussed as emulsifiers, de-emulsifiers, cleaners, wetting, dispersing, and foaming agents (Moya Ramirez et al. 2015; Gudiña et al. 2016), in bioremediation of soil and sand (Van Dyke et al. 1991), and in the cleanup of hydrocarbon contaminated groundwater and enhanced oil recovery (Ron and Rosenberg 2001) (section “Applications of Rhamnolipids”).

Compared to oil-based surfactants, biosurfactants are typically composed of a set of different molecules. Therefore the surface activity of, e.g., rhamnolipids described in literature varies as different production processes, and purification steps were used leading to different compositions.

Important physicochemical characteristics of biosurfactants for applications are their surface tension, critical micelle concentration, foaming behavior, wetting properties, and emulsification activity. Biological properties as, e.g., biodegradability, ecotoxicity, skin compatibility, and potential antimicrobial activity are also important for applications and are described in section “Applications of Rhamnolipids.”

In the following, methods are described to determine the physicochemical properties and the respective data reported for rhamnolipids. In most studies, only mixtures of rhamnolipids were analyzed, while congener properties are rare to date.

3.1 Surface Tension

The surface tension , usually represented by the symbol γ, is the cause of the behavior of liquids, such as water, to form energetically favorable spherical drops. The dimension is given in force per unit length [N/m]; in some older publications, [dyn/cm] is also used, where 1 mN/m corresponds to 1 dyn/cm. Pure water has a relatively high surface tension of 72.8 mN/m at 20 °C. The reduction of surface or interfacial tension, especially of water-based formulations, facilitates the wetting of solid surfaces and improves the stability of emulsions and dispersions. This is important for applications like printing, coating, cleaning, or the dispersion of pigments. There are several methods to measure the equilibrium or dynamic surface tension or interfacial tension, e.g., Wilhelmy plate method, Du Nouy ring method (Varjani and Upasani 2016), bubble pressure method, or drop volume method. For liquids with higher viscosity or if only very small amounts of liquid are available, the pendant drop measurement with drop shape analysis is a good alternative. The surface tension of surfactant solutions depends on the temperature and, for biosurfactants with ionizable groups, the pH value.

Rhamnolipids are reported to reduce the water surface tension from 72 to 35, 28 mN/m, or even lower values (25.9 mN/m) (Ma et al. 2016). The studies used different producer organisms, growth substrates, and fermentation processes and solutions with different pH values and concentrations of biosurfactant (Paulino et al. 2016; Varjani and Upasani 2016). Nevertheless, the values are in the range of sodium dodecyl sulfate (SDS), a very effective and often used surfactant.


Another important primary characteristic of a surfactant is the critical micelle concentration (CMC). It is defined as the concentration of surfactants above which micelles form and surfactant monomers and micelles exist in a dynamic equilibrium (Dominguez et al. 1997). It provides good insights into the nature of the surfactant’s self-association. Low CMC values indicate that the minimum surface tension is reached with lower amounts of the surfactant, and therefore the surfactant is more efficient. The CMC value depends on temperature, pH, salt concentration, and presence of organic impurities. For surfactants with defined and known structure, the CMC is often given in mol/L; for biosurfactants, the dimension mg/L is used. Especially during process optimization, the critical micelle dilution (CMD) is often used to characterize non-purified products. Here, a cell-free supernatant is diluted tenfold (CMD−1) and 100-fold (CMD−2) (Makkar and Cameotra 1998; Bordoloi and Konwar 2008) for measurements of surface tension.

The methods for CMC determination include measuring of conductivity, solubility, viscosity, light scattering, and surface tension (Song et al. 2015), of which the determination by the use of tensiometers is the most popular one. Typically, these measurements are performed with a Wilhelmy plate and an automated dosing accessory. The measured surface tension as a function of the logarithmic bulk surfactant concentration will result in a curve that can be fitted with two straight lines with the CMC at their intersection.

For rhamnolipids reported CMC values are between 230 mg/L for rhamnolipid mixtures with higher proportion of congeners with unsaturated fatty acids (Abalos et al. 2001) and 5 mg/L (Syldatk et al. 1985; Dubeau et al. 2009; Costa et al. 2010; Gogoi et al. 2016). The CMC value of 5 mg/L was reported by Nitschke et al. (2005) for di-rhamnolipid Rha-Rha-C10-C10, while the mono-rhamnolipid Rha-C10-C10 reached 40 mg/L. Rhamnolipids obtained by Gudiña et al. (2015) showed CMC values between 10 and 200 mg/L; Ma et al. (2016) found 50 mg/L for their rhamnolipids. In general, low CMC values (11–20 mg/l) are observed in mixtures containing mainly mono-rhamnolipid with C10 fatty acids (Guo et al. 2009). The CMC strongly depends on the producing microorganisms. In single-strain cultures, Hošková et al. (2015) measured for rhamnolipid mixture produced by P. aeruginosa a CMC value of 56 mg/L, while rhamnolipids produced by A. calcoaceticus and E. asburiae revealed values of 15 and 21 mg/L, respectively. For comparison, the CMC for SDS in water is ten to hundred times higher with a value of 2100 mg/L.

3.3 Emulsification Activity

The emulsification activity or index (E24) is used to characterize emulsifying properties of biosurfactants, generally for oil-in-water (o/w) emulsions. It is often used as an indirect method to screen biosurfactant production (Thavasi et al. 2011). It was first described by Cooper and Goldenberg (1987) to measure the emulsifying activity of biosurfactants from Bacillus species. They vortexed for 2 min a defined volume of aqueous biosurfactant solution with a defined volume of a nonmiscible liquid of interest, in their investigation kerosene. They defined the emulsion index E24 as the height of the emulsion layer after 24 h, divided by the total height, multiplied by 100. Some authors extended the time to 30 days to study long-term behavior (Varjani and Upasani 2016). The values strongly depend on the experimental setup; nevertheless, the index gives indicative results concerning emulsifying behavior.

Investigations on rhamnolipids obtained from P. aeruginosa DN1 showed excellent emulsification activity in the order of 100% to several hydrocarbons (Ma et al. 2016). Gudiña et al. (2015) measured emulsification indices in the order of 60–70% using n-hexadecane. Rhamnolipids produced by P. aeruginosa SP4 (Pornsunthorntawee et al. 2008) were found to exhibit excellent emulsification properties for vegetable oils (palm oil, soybean oil, coconut oil, and olive oil) but failed to emulsify short-chain hydrocarbons (pentane, hexane, heptane, toluene, and 1-chlorobutane).

3.4 Foaming Behavior

All surface-active substances tend to build foams when gas is introduced into the liquid phase. The foaming behavior of biosurfactants is vital for many industrial applications. For some applications, the formation of foams is desirable, e.g., in body care, culinary foams, flotation, and firefighting. However, in many applications foaming is unwanted and must be prevented, e.g., in printing and coating, cooling lubricants, liquid conveying, industrial cleaning, or during fermentation processes. Particular areas of application lead to different requirements for foamability, foam stability, moisture content, and the size of bubbles in the foam. Over the past decades, researchers have developed many empirical tests to evaluate foaming performance. Methods include the Rudin test used in the brewing industry (Rudin 1957), Bikerman test (Bikerman 1973), Ross-Miles method (Ross and Miles 1941), confocal microscopy method (Koehler et al. 2004), resistance-strengthening technology (Barigou et al. 2001), and others. The most common of these is the Ross-Miles method. The foamability of surfactant solutions and the stability of the foam produced are determined based on height measurement (Lunkenheimer et al. 2010). Several international standards were deviated from the method, of which ASTM D 1173 “Standard Test Method for Foaming Properties of Surface-Active Agents” is the one closest to the original publication.

During the fermentation of rhamnolipids, strong foaming is observed, which limits the yield and therefore increases production costs. Rhamnolipids are discussed as the dominant component that causes the severe foaming during fermentation (Zhang and Ju 2011). Alternatively, foam fractionation is suggested as in situ product removal method, hence taking advantage of the foamability of rhamnolipids (Siemann-Herzberg and Wagner 1993; Blank et al. 2013b; Küpper et al. 2013; Beuker et al. 2016a). In a recent systematic study, Long et al. (2016) demonstrated that purified rhamnolipids show a foaming behavior close to SDS, a very strong foaming agent, but only if additional stirring was applied. With the classical Bikerman test, the rhamnolipid showed a comparable foam stability as Tween 20, which is well known for its poor foam stability.


The hydrophilic-lipophilic-balance (HLB) number was introduced by Griffin and coworkers (Griffin 1949, 1954) to classify nonionic surfactants according to their emulsifying properties: the higher the HLB number, the more hydrophilic (water soluble) and the lower the HLB number, the more lipophilic (oil soluble) the surfactant will be. The system was developed for ethoxylated surfactants, and the transferability of the concept to other surfactant structures is critically discussed in the literature. Nevertheless, it is an often used concept to select surfactants for specific formulations. In general, surfactants with HLB 4–6 are used to stabilize water-in-oil (w/o) emulsions, with HLB 8–12 for oil-in-water (o/w) emulsions, and with HLB 13–15 to formulate detergent solutions. The HLB can be calculated if the structure is known or determined experimentally by different methods, e.g., 1H-NMR, dielectric constant, titration of phenol, gas chromatographically, or colorimetrically (Rabaron et al. 1993).

Another approach to select suitable surfactants for microemulsions is the hydrophilic–lipophilic deviation (HLD), a dimensionless number expressing the difference of affinity of the surfactant for the oil and water phases (Nardello et al. 2003; Witthayapanyanon et al. 2008).

No data on HLB or HLD numbers for rhamnolipids can be found in literature. Long et al. (2013) stated for rhamnolipids a HLB number of 10.9, unfortunately without details about experimental data or information about the investigated rhamnolipid.

For the application of rhamnolipids in, e.g., cosmetics or drug delivery products, knowledge about the HLB or HLD numbers is very important for a developer of formulations (Schmidts et al. 2010). Therefore, the determination of these numbers should be addressed in future works.

4 Applications of Rhamnolipids

The physicochemical properties described above suggest many possible applications for rhamnolipids also indicated by a high number of scientific publications as well as patents which have been summarized in excellent reviews (Lang and Wullbrandt 1999; Maier and Soberon-Chavez 2000; Irfan-Maqsood and Seddiq-Shams 2014; Paulino et al. 2016).

The first application for rhamnolipids after their discovery in 1963 (Burger et al. 1963) emanated in the late 1980s (Linhardt et al. 1989). Among the first patents, several described the production of l-rhamnose from rhamnolipids (Mixich et al. 1990). From this point on, rhamnolipids were used for a broad range of different applications, for various market sizes and requirements in terms of product purity. For example, different purities of rhamnolipids are suggested for the enhancement of crude oil recovery and in pharmaceutical applications. Up to 2010, rhamnolipids remained the only biosurfactants that have been approved for the use in food, cosmetic, as well as in pharmaceuticals (Toribio et al. 2010).

The annual worldwide consumption of chemical surfactants in 2012 was estimated to be in the order of 13 million tons (Marchant et al. 2014). In 2013, the biosurfactant market was around 350 thousand tons from which at least two thirds were artificially synthesized surfactants as methyl ester ketones and alkyl polyglucosides (Gran View Research 2015). Hence, the contribution of microbial biosurfactants to the total surfactant market is lower than 2%, indicating a huge remaining market potential.

4.1 Applications with Environmental Concern

Among the most promising applications for rhamnolipids identified so far are those related to environmental concerns , such as bioremediation and enhanced oil recovery (Nitschke et al. 2005). Additionally, rhamnolipids find applications in agriculture.

4.1.1 Microbially Enhanced oil Recovery

Microbially enhanced oil recovery (MEOR) exploits specific traits of microorganisms to enhance oil recovery from oil wells, especially in tertiary oil recovery (Raiders et al. 1989). Two methods for MEOR exist. Ex situ MEOR uses culture broth gained from classical fermentations, which is injected into the oil reservoir. In in situ MEOR, the reservoir is inoculated with the bacteria itself (Paulino et al. 2016). Using ex situ MEOR is a selective method, which only requires small quantities of the surfactant and has a broad application range (oil type and reservoir conditions) (Irfan-Maqsood and Seddiq-Shams 2014). For both types of MEOR, lab experiments resulted in promising results. In situ experiments were, for example, carried out using Pseudomonas aeruginosa F-2 on oily sludge (Yan et al. 2012). The challenges are manifold, as many of the rhamnolipid producers are non-fermentative, but, like P. aeruginosa, can use alternative electron acceptors like nitrate and sulfur compounds, possibly contained in crude oil.

4.1.2 Bioremediation

There are different types of contaminations (mainly from anthropogenic origin) that can be remediated with the help of rhamnolipids with the most obvious being hydrocarbons, but the reduction of heavy metal contamination with rhamnolipids is also discussed (Nitschke et al. 2005). Hydrocarbon Pollutions

Applying rhamnolipids for bioremediation has been tested intensively. Under laboratory conditions enhancement of the degradation of a whole range of different substrates could be shown. Hexadecane and octadecane were degraded using Pseudomonas strains (Desai and Banat 1997), n-paraffin, and phenanthrene (Maier and Soberon-Chavez 2000), and the herbicide atrazine by Acinetobacter (Singh and Cameotra 2014).

In principle, two methods are feasible for the remediation of contaminated soils: degradation of the pollutants and flushing/washing of soils.

Flushing of hydrocarbons from contaminated sandy loam and silt loam soil could benefit from the application of rhamnolipids (Van Dyke et al. 1993). The removal of aliphatic and aromatic hydrocarbons (Scheibenbogen et al. 1994), as well as polyaromatic hydrocarbons, and pentachlorophenol (Sachdev and Cameotra 2013) was also increased by adding rhamnolipids. Flushing of soils enhanced by rhamnolipids furthermore showed removal of hexadecane, octadecane, phenanthrene, pyrene, polychlorinated biphenyls, a variety of PAH, and hydrocarbon mixtures (Maier and Soberon-Chavez 2000) as well as crude oil (Lang and Wullbrandt 1999).

For the remediation of oil spills like in the Gulf of Mexico in 2010, vast amounts of detergent are required. After the Exxon Valdez oil spill in 1989, it could be shown that rhamnolipid-aided large-scale in situ bioremediation by washing was successful for the removal of oil from contaminated Alaskan gravel (Harvey et al. 1990; Bragg et al. 1994).

Rhamnolipid-aided degradation of hydrocarbons was shown for hexadecane, pristine, tetradecane, creosote, and hydrocarbon mixtures (Maier and Soberon-Chavez 2000). In addition, natural breakdown of hydrocarbons in marine oil pollution was demonstrated to benefit from rhamnolipid application (Lang and Wullbrandt 1999).

Rhamnolipids may stimulate the indigenous bacterial population to degrade hydrocarbons at increased rates (Desai and Banat 1997). Mechanisms include increased hydrocarbon availability by forming rhamnolipid-fostered emulsions (Maier and Soberon-Chavez 2000). Another effect might be the interaction with the cell surface to make it more hydrophobic, which causes the cells to associate more easily with the hydrocarbons (Maier and Soberon-Chavez 2000). To explain the enhancement of oil degradation by washing, it has been speculated that above the CMC, hydrophobic compounds can diffuse into the center of the micelles (Paulino et al. 2016), which can then be flushed more easily. All in all, this leads to the efficient breakdown and removal of pollutants from contaminated areas aided by rhamnolipids. Thus, less surface active agents have to be introduced into the polluted areas (Nitschke and Costa 2007) diminishing the negative impact on nature even further. Bioremediation of sites polluted with hydrocarbons is therefore an important field of application for rhamnolipids, as here low requirements regarding purity exist and thus production costs remain low. Metal Pollutions

Contaminations with metals and heavy metals are not easily remediated. Metal contamination in soils is, for example, caused by the use of metal salt-based fungicides. However, in higher concentrations, they can cause damage to plants, making it important to remove the metals from the soil. Another important field of application for the removal of metal pollutions is the bioremediation of former industrial sites.

Rhamnolipids have been shown to be able to remove Cd, Pb, and Zn from soil (Gautam and Tyagi 2006). Also metals such as Ba, Ca, Cu, Li, Mg, Mn, and Ni could be washed from soil (Sachdev and Cameotra 2013). A technique called micellar-enhanced ultrafiltration was applied for the successful removal of Cd, Cu, Ni, Pb, and Zn (El Zeftawy and Mulligan 2011). Rhamnolipid-enhanced flushing of soils was used for the removal of Cd, Cu, La, Pb, and Zn (Maier and Soberon-Chavez 2000).

Metal organic co-contaminated sites could be partially cleaned when rhamnolipids were added to the cleaning solution. In lab experiments, the degradation of naphthalene in a culture co-contaminated with cadmium was shown. In experiments using real soils, hydrocarbon degradation was enhanced in soils contaminated with cadmium and phenanthrene (Maier and Soberon-Chavez 2000).

The general mechanism for the removal of metals from soils is solubilization and subsequent washing. A proposed mechanism may involve a combination of complexation of the heavy metals with the rhamnolipid molecules and interaction with the cell surface to alter uptake of heavy metals (Ron and Rosenberg 2001; Gautam and Tyagi 2006). Complexes formed can easily be washed from the soil matrix (Christofi and Ivshina 2002). As in the hydrocarbon pollution, the micelle-forming capabilities help in heavy metal remediation. The polar heads of the surfactant in the micelles can bind to metals and facilitate desorption of the metal ions from the soil. The metal ions in emulsion can then be removed by flushing (Kiran et al. 2016). Apparently, also the remediation of sites polluted with metals can benefit from the addition of rhamnolipids. Moreover, rhamnolipid-aided remediation can also cope with co-contaminations, which make these glycolipids a powerful tool for a whole range of bioremediation applications.

4.1.3 Agriculture

The applications of detergents in agriculture are manifold, including their use as antifoam , superspreader , and active ingredient. Rhamnolipids can be applied on the soil or on the plant itself. The main impact of the rhamnolipids on plantations are their anti-pathogenic effects, which they feature regardless if introduced into the soil or sprayed on the plant.

The soil furthermore benefits by an improved quality, caused by the decrease in plant pathogens and an increase in nutrient availability (Paulino et al. 2016). Their positive effects on the rhizosphere were, for example, demonstrated by reducing damping-off disease in plants (Sharma et al. 2007a, b). As stated above rhamnolipids also help to improve soil quality by remediation of different pollutants, which is mainly done by solubilization of the hydrophobic molecules and increasing their bioavailability. The same mechanism acts on hydrophobic nutrients, thus increasing the uptake of these compounds by the plant. In addition, the wettability of soils can be increased by surfactants, leading thus to a better distribution of fertilizers.

On plants, rhamnolipids also serve as anti-plant pathogenic compounds by prohibiting growth of certain plant pathogens. Examples can be found in the successful treatment of Nicotiana glutinosa infected with tobacco mosaic virus or of Nicotiana tabacum for the control of potato virus X disease (Haferburg et al. 1987).

Rhamnolipids also show antifungal effects , which is why they are the active substance in the US EPA approved Zonix fungicide (Jeneil Biosurfactants Co., Saukville, USA) (Müller et al. 2012). They are effective against Fusarium oxysporum wilt disease in tomato plants (Deepika et al. 2015) and inhibit zoospore-forming plant pathogens that have acquired resistance to commercial chemical pesticides (Sachdev and Cameotra 2013). For example, zoospores of the oomycete pathogen Phytophthora capsici, which is the causative agent of the damping-off disease of cucumber are lysed by rhamnolipids (Kruijt et al. 2009). Also the zoosporic plant pathogens Olpidium brassicae, Phytophthora capsici, Plasmopara lactucae-radicis, and Pythium aphanidermatum are effectively deactivated (Maier and Soberon-Chavez 2000). Furthermore, rhamnolipids can be used to prevent adhesion of microbes to roots and reduce bacterial biofilm formation (Haba et al. 2003). Another trait beneficial for agriculture is the insecticidal activity of rhamnolipids, for example, against the green peach aphid (Myzus persicae) (Kim et al. 2011).

Furthermore, rhamnolipids can mediate resistance against microbes by stimulating the plant immune system (Vatsa et al. 2010; Sanchez et al. 2012). This effect potentially facilitates the use of rhamnolipids as so-called priming agents. For priming, the surfactant is applied to the seeds prior to plantation. The plant subsequently develops immune responses against certain pathogens although the rhamnolipid is not present anymore. The mechanism of rhamnolipid action remains to be elucidated. However, rhamnolipids have more beneficial effects if applied to seeds. da Silva et al. (2015) showed an increase in germination rate of lettuce and corn, while soybeans showed increased seedling development.

A possible mechanistic explanation why rhamnolipids are more effective as chemical surfactants might be that rhamnolipids enhance the foliar (leaf) penetration of soluble molecules and the leaf wettability and surface properties (Liu et al. 2016). Thus, the plant can take up the biosurfactant more effectively.

In summary, rhamnolipids exert numerous effects when applied in agriculture with the main benefit being the use as anti-plant pathogenic agents. Since plant vermin causes tremendous losses, a huge market potential exists for rhamnolipids as plant protection agents.

4.2 Applications for Consumer Goods

Another broad field of rhamnolipid applications comprises its use as additive in consumer goods, namely, food , cosmetics, household detergents, and even medicinal products. Here, we briefly summarize some applications mentioned in the literature.

Rhamnolipids are applied in the food industry and also in medical fields because of their high potential to inhibit biofilm formation (for a mechanistic explanation, see “Biological Control”) (Paulino et al. 2016). In the food industry, biofilms are encountered on processing devices, where they pose a potential threat for hygiene. In medical applications, biofilms growing, for example, on implants represent a major threat for the patients.

4.2.1 Food

Rhamnolipids are discussed as natural food additives, which can replace chemicals as they are of biological origin and can thus easily comply with the guidelines for natural organic foods. Rhamnolipids are reported to control consistency, which is important for the sensual enjoyment, delay staling, solubilize flavor oils (Nitschke and Costa 2007), stabilize fats, and reduce spattering (Kosaric 2001). They have already been applied to improve texture and shelf life of starch-containing products (Nitschke and Costa 2007). In addition, rhamnolipids can modify the rheological properties of wheat dough and may be used to improve the consistency and texture of fat-based products (Kachholz and Schlingmann 1987). Properties of products such as butter cream, croissants, and frozen confectionery also benefit from the addition of rhamnolipids (Irfan-Maqsood and Seddiq-Shams 2014).

4.2.2 Cosmetics

Surfactants in general are widely applied in the cosmetics industry (Klekner and Kosaric 1993). As biosurfactants are believed to have a higher skin compatibility and only low skin irritation potential, they feature advantages over synthetic surfactants (Haba et al. 2003). Rhamnolipids are specifically mentioned in patents for the production of liposomes and emulsions (Maier and Soberon-Chavez 2000). Here, the pronounced emulsifying activity of rhamnolipids is beneficial for the texture of cosmetic products (Haba et al. 2003).

Rhamnolipids have already been applied as cosmetic additives (Maier and Soberon-Chavez 2000) and in health care products in several different formulations, for example, insect repellents, antacids, acne pads, anti-dandruff products, contact lens solutions, deodorants, nail care products, and toothpastes (Lourith and Kanlayavattanakul 2009). Also cosmetics as anti-wrinkle and antiaging products were produced in several dosage forms as commercial skin care cosmetics using rhamnolipids (Lourith and Kanlayavattanakul 2009). Rhamnolipids exert a broad range of functions including emulsifying and antimicrobial activity (e.g., in acne pads). The increased availability of rhamnolipids will foster further testing; hence, we expect many more applications in the future.

4.2.3 Pharmaceuticals

Rhamnolipids are in general suited for medical applications as they show antibacterial , antiphytoviral (Rodrigues et al. 2006), and excellent antifungal properties (Abalos et al. 2001). In addition, they are reported to stimulate the immune system of animals (Vatsa et al. 2010). They furthermore can mediate the disruption of established biofilms (Marchant and Banat 2012) or inhibit the adhesion of yeasts and bacteria to voice prostheses (Rodrigues et al. 2006).

Antimicrobial effects of rhamnolipids were demonstrated against Serratia marcescens, Enterobacter aerogenes, Klebsiella pneumoniae, Staphylococcus aureus and Staphylococcus epidermidis (Haba et al. 2003), Bacillus subtilis (Wittgens et al. 2011), Escherichia coli, Micrococcus luteus, Alcaligenes faecalis, Rhodococcus erythropolis, Bacillus cereus, Mycobacterium phlei (Irfan-Maqsood and Seddiq-Shams 2014), and Listeria monocytogenes (Magalhães and Nitschke 2013); here, combination with nisin resulted in a synergistic effect.

Antifungal properties were shown against Chaetomium globosum, Penicillium funiculosum, Gliocladium virens, Fusarium solani (Haba et al. 2003), Aspergillus niger, Chaetosphaeridium globosum, Penicillium chrysogenum, Aureobasidium pullulans, Botrytis cinerea, Rhizoctonia solani (Abalos et al. 2001), and Penicillium crysogenum (Irfan-Maqsood and Seddiq-Shams 2014). Mycelial growth of Phytophthora sp. and Pythium sp. was also impeded (Irfan-Maqsood and Seddiq-Shams 2014). Rhamnolipids are furthermore effectively inhibiting growth of the algae Heterosigma akashiwo and Protocentrum dentatum (Wang et al. 2005). However, mono-rhamnolipids showed low toxicity against Aspergillus niger spores during the germination and Candida albicans (Johann et al. 2016).

The antimicrobial effects of rhamnolipids were proposed to be caused by intercalation into the cell membrane resulting in increased permeability and subsequent cell death (Sotirova et al. 2008).

Rhamnolipids were specifically applied to enhance healing of burn wounds. They increase the wound closure time and, as they inhibit the activity of fibroblasts, decrease the collagen content in the wound, which leads to lesser scar formation (Stipcevic et al. 2006). In addition, they were successfully used to treat ulcers caused by the stimulation of bone marrow (Piljac et al. 2008). In vitro experiments also showed antitumor and antiproliferative properties, which might be caused by the reduction of surface tension of the culture medium (Paulino et al. 2016). In vivo experiments are thus crucial to confirm these effects. In human skin, rhamnolipids were demonstrated to induce the production of psoriasin, an antimicrobial protein (Meyer-Hoffert et al. 2011). Rhamnolipids were also applied to treat tuberculosis infections (Irfan-Maqsood and Seddiq-Shams 2014) and psoriasis (Piljac et al. 2008).

Pharmaceutical applications can also benefit from a trait described above. Rhamnolipids can be used to stabilize liposomes, which are pH sensitive and thus suited for transport of substances into cells (Sanchez et al. 2010) and have been successfully applied to produce microemulsions for drug delivery (Nguyen et al. 2010).

4.2.4 Household Detergents

Rhamnolipids as amphiphilic molecules are well suited for the use as detergents, e.g., in household cleaners. Detergents often end up in the environment, where they potentially harm ecosystems. The advantage of rhamnolipids over synthetic chemical detergents is their low ecotoxicity and furthermore their biodegradability, diminishing their impact on the environment even more.

Rhamnolipids are discussed as environmentally friendly cleaning agents (Randhawa and Rahman 2014) as was shown in cleaning soap mixtures (Ecover products); comparable results were obtained with commercial washing powders (Khaje Bafghi and Fazaelipoor 2012). The companies Evonik and Unilever filed patents for the use of rhamnolipids for textile washing (Parry et al. 2012; Kuppert et al. 2014).

4.3 Biological Control

As stated above, rhamnolipids are effective against a variety of microorganisms. This property renders them suited for a couple of biocontrol applications. As they are capable of removing and even destructing biofilms of several Gram-positive and Gram-negative bacteria (Paulino et al. 2016), they were, for example, applied in the cooling system of an atomic power plant (Dusane et al. 2011) as well as for devices in the food and pharmaceutical industry (Paulino et al. 2016).

The prevention of biofilm formation effected by rhamnolipids was proposed to be caused by modifications of the surface hydrophobicity and interference in adhesive properties of the bacteria (Paulino et al. 2016). The destruction of already existing biofilms might be caused by the alteration of the biofilm environment and the removal of extracellular polymeric substances (Paulino et al. 2016).

4.4 Specialty Applications

Apart from the obvious applications based on the surface-active properties of rhamnolipids, a few applications have been published, for example, in the production of fine chemicals (Banat et al. 2000).

4.4.1 Fine Chemicals

Rhamnolipids can serve as precursor molecules for the production of fine chemicals , e.g., to synthesize enantiopure l-rhamnose for the production of high-quality flavor compounds and as chiral precursor for active agents or as hydrophilic carrier for the transport of insoluble drugs in humans (Linhardt et al. 1989). Further, to determine specific properties of solid surfaces, a pyrenacylester was synthesized from rhamnolipids to facilitate the use of pyrene (Ishigami and Suzuki 1997).

4.4.2 Nanoparticle Synthesis

Furthermore, biosurfactants can be used for high-performance nanomaterial production, since they easily form a variety of liquid crystals in aqueous solutions (Kiran et al. 2016). These nanoparticles could, for example, be used to deliver drugs (Dahrazma et al. 2008). Kiran et al. demonstrate successful synthesis of nanozirconia particles and silver nanoparticles aided by rhamnolipids, which proved to be more effective than chemical surfactants (Kiran et al. 2016). Rhamnolipid-mediated synthesis of NiO nanoparticles led to a decrease in nanoparticle size (Palanisamy and Raichur 2009).

5 Patent Landscape

5.1 Patent Analysis and Its Applications

In its core, patent analysis is a family of techniques that employs patent data to derive information about a particular industry or technology field. The advantage of using such data lies in the amount of structured and easily accessible information which patents contain clear identification of authors, jurisdictions, assignees, and technological domains. As a strategic tool, patent analysis can be used for monitoring emerging developments such as convergence between industries (Curran et al. 2010; Bornkessel et al. 2014). In more practical terms, patents carry business and legal implications and are usually associated with considerable costs. These characteristics make them an indicator for high interest and potential investment, as well as a basis for various policy or corporate decisions.

For the purpose of this chapter, patent data is employed to build a landscape of technological areas and trends that are of importance to rhamnolipids and their application. Key industrial sectors and companies are also outlined. Results, however, should be interpreted with caution as legal practices, and patenting behaviors differ around the world and across industries. Additionally, the value distribution of patents is highly skewed; many have no industrial application, whereas few are highly valuable (Hall et al. 2005).

As there are various documents published at different stages during the patenting procedure, a few key terms ought to be defined: patent application refers to a pending request at a patent office for a patent to be issued, while patent grant is the intellectual property right granted by the respective patent office to the inventor. Furthermore, patent family denotes a group of documents published in different countries (or languages) but referring to the same invention. International Patent Classification (IPC) codes are a hierarchical system of symbols that classifies patents according to the different areas of technology to which they apply (all definitions follow the World Intellectual Property organisation (Trippe 2015)).

5.2 Patenting Activity and Assignee Structure

As mentioned in a previous section, the discovery of rhamnolipids happened in 1963 and led to actual application in the late 1980s. The time development of the patenting activity between 1985 and 2015 can be seen in Fig. 3. A pattern of peaks and fast decreases can be observed, with the first peaks being in 1988 and 1993 (27 and 45 filed applications, respectively), followed by a period with relatively low activity (the average number of patent applications between 1995 and 2001 is 12 per year). In 2003, the number of filed documents almost equals the peak from 1993, and in 1997 this number reaches 50. During the period 2009 to 2014, patent applications are steadily increasing, and it is in this time frame that 48% of all applications in the sample were filed. After the year 2014, however, the number starts to decrease again.
Fig. 3

Number of rhamnolipid patent documents per year between 1985 and 2015. N = 890 applications and 292 grants

To aid the interpretation linear trend lines are introduced to demonstrate the general growth in patent documents. This overall positive development indicates an increasing interest and innovation effort in the synthesis and/or use of rhamnolipids.

The curve of granted (issued) patents somewhat follows the one in patent applications but with a significant delay, as the average time to obtain a grant for this specific sample is above 1500 days (more than 4 years). Furthermore, not all pending requests result with a patenting right – the average ratio between filed applications and issued patents in this sample is roughly 3:1.

A closer look at the patent assignees’ structure reveals a total of 249 individuals, companies, universities, and research institutes that have applied for intellectual property rights on their innovations (110 of them with granted rights). The analysis of such data can give valuable indications of the most active “players” in the field of rhamnolipid synthesis and use. A list of those assignees that have ten or more patent applications is presented in Fig. 4. According to their core activities, they can be further divided into the following groups:
Fig. 4

Assignees with ten or more filed applications

Chemistry and Biochemistry

The patent data reveals that this is the most relevant industry sector for rhamnolipids and their production or application. Combined, the six companies hold a total of 217 patent applications and 62 grants (or 23% of all applications and 19% of all granted patents in the set). The most active assignee in the group, Evonik, possesses 59 pending and five issued patents. Second comes Jeneil Biotech, a company focused on food ingredients, with 56 applications and ten grants, followed by Aventis Gmbh, Stepan Co., and Synthezyme LLC (39, 28, and 20 filed applications, respectively). Last in the group is DuPonts Danisco Inc. with 15 applications and no granted patents yet.

Consumer Goods, Cosmetics, and Food

The group includes Unilever, which is the most active patent assignee, holds a total of 75 applications and 23 granted documents. The multinational giant is followed by three companies with 11 filed applications each, namely, the sugar producer Südzucker AG, the cosmetics manufacturer and seller Avon, and Clorox that is famous for its cleaning products. Last, with ten applications each, come Ecover and Procter & Gamble Co. Combined, the companies from this group account for 128 filed and 43 granted patent documents (around 13% of the documents set).


Two companies are listed here, the biopharmaceutical producers Paratek Pharmaceuticals Inc. and Paradigm Biomedical Inc. that focuses especially on products derived from rhamnolipids. Together they have a total of 60 applications and 27 issued patents.

Academic Research

Four of the most active assignees come from the academic field, namely, Adelaide Research and Innovation Pty. Ltd. (consulting services for the University of Adelaide), Montana State University, University of Hunan, and Energy and Resources Institute TERI. Together the group accounts for 48 patent applications and 26 granted documents. In fact, nearly 30% of all assignees in the whole sample represent universities or research institutes. Moreover, although a quarter of them have filed only one patent application, 45% of these requests have resulted in grants (as opposed to the 32% for the assignees that are companies or individuals).


The group features two companies from the oil sector – Idemitsu Kosan Co. Ltd., Wintershall AG (subsidiary of BASF), and Tajco Inc. that comes from the automotive industry. They possess 41 applications and 21 issued patents in total (or 4% of the applications and 7% of the grants in the sample).

5.3 Application Areas Based on IPC Codes

As defined above, International Patent Classification (IPC ) codes are a hierarchical system of language-independent symbols that define the technological field a patent relates to. An analysis of the codes most frequently associated with rhamnolipids reflects the list of major applications given in section “Applications of Rhamnolipids”. To illustrate this notion, the IPC codes were grouped according to these areas and can be seen on Table 2.
Table 2

Grouping of IPC codes and applicational areas

Applicational area

IPC codes

Meaning of the IPC code

Number of patent applications

Application in the field of chemistry and biochemistry



Acyclic or carbocyclic compounds




Heterocyclic compounds




Sugars and derivatives




Microorganisms and enzymes








Processes involving enzymes and microorganisms




Biochemistry, enzymology, beer, spirits, wine, vinegar


Application with regard to environmental issues

Oil recovery


Treatment of water/sludge




Recovering of oils from shale, sand, or gases




Treating contaminated soil




Preservation of bodies (human, animal, plants)




Biocides and pest repellants










Consumer goods

Food and feed


Food and preservation of food




Animal feed








Medical, dental, and toilet purposes




Sterilizing materials, bandages, and dressings




Medicinal preparations




Detergent compositions


Applications with Respect to Environmental Concerns

Innovations that refer to the emulsification abilities of rhamnolipids are mostly classified with the code C02F (corresponds to the area treatment of waste water) or B09C (corresponds to remediation of contaminated soil). Patents in this group feature, for example, environmentally friendly treatment of oil spills, or production methods for heavy metal biological absorbents. The assignee that has applied for the most patent documents in this application area is not a commercial entity, but the State University of Montana. Meanwhile, the use of rhamnolipids in the sphere of agriculture is denoted by classes A01P (biocides and repellents), C05D/C05G (corresponding to the area of fertilizers), and A01N (preservation of bodies). Jeneil Biotech and its subsidiaries are the most active applicants in the subgroup.

Applications with Respect to Consumer Goods

The patent data confirms the proposition that rhamnolipids cater for a variety of industrial demands in the area of consumer goods. Subclasses A61K, A61Q, A61L, A61P (assigned to patents in the field of medical science, hygiene, or cosmetics), and C11D (detergent compositions) account for a substantial share of patent applications. Additionally, class A23 (food or foodstuff) can be included, as it corresponds to the application of rhamnolipids in food preservation and in animal feed. Unsurprisingly, Unilever is the company with the most filed applications in this group.

Applications Referring to Biological Control

No concrete IPC code corresponds directly to this area of application, but adding “biofilm” as a keyword in the search string results in 84 filed and 26 issued patents, the key IPCs being A61K, A61P, and A01N. The most prominent companies in this specific field are Paratek Pharmaceuticals and Synthezyme LLC with eight and five granted patents, respectively.

IPC Groups Referring to (Bio)chemistry and Related Activities

In addition to the areas described so far, there are a few IPC codes that are assigned to the majority of rhamnolipid-related patents as they belong to the field of chemistry. Namely, these are the classes C07 and C12.

Finally, it is not only the application of rhamnolipids that attracts the attention of businesses and researchers but also their production. A manual scan of the 364 patent families obtained reveals that between 20% and 30% of them relate to innovative methods for the synthesis of rhamnolipids. Most of these patents focus on up- and downstream processing, different wastes as substrates for rhamnolipid synthesis, and medium compositions. In addition, high titers and yields are often claimed to be achieved, while only few patents mention the use of recombinant bacteria. It can thus be stated that apart from the application of these remarkable biosurfactants, also the production of rhamnolipids is a highly active field in the actual patent landscape.

6 Research Needs

At the moment, high production costs still represent the major drawback preventing a more widespread application of rhamnolipids and biosurfactants in general (Marchant and Banat 2012b). To foster the industrial use of rhamnolipids, production costs will have to be significantly decreased by further genetic engineering of the biocatalyst, optimization of fermentation procedures, and integrating affordable downstream processing.

Another challenge in the use of these alternative biosurfactants is that each organism produces a mixture of congeners with a range of different structures and therefore properties but is nonetheless metabolically limited to a particular set of congeners (Roelants et al. 2013). The production of rhamnolipid mixtures with a specific composition adapted to desired physiochemical properties should be explored in the future by mixing lipids from different organisms and engineering producer strains or by producing tailor-made mixtures in vivo by choosing the respective strain biosynthetic operons and/or combining producers strains for production as already outlined by Hošková et al. (2015).

7 Concluding Remarks

A number of bacteria are able and applied to produce rhamnolipid biosurfactants, depicting a mix of different congeners. Remarkably, the rhamnolipid mixtures produced by different strains do not necessarily show the same composition but may differ regarding their particular set of rhamnolipid molecules, whereas, for example, most P. aeruginosa rhamnolipid mixtures constitute mixtures of mono- and di-rhamnolipids with predominantly C10-chains (Déziel et al. 1999); Burkholderia sp.-derived mixtures seem to be dominated by di-rhamnolipids, which contain HAA with longer (around C14) chains (Manso Pajarron et al. 1993; Dubeau et al. 2009; Díaz De Rienzo et al. 2016). Shorter chains are described for P. desmolyticum-derived species (Jadhav et al. 2011). The different fatty acid spectra may be attributable to specificities of rhlA (Blank et al. 2013a), and also supplied carbon sources may influence the final chain length. Furthermore, differences in the genetic organization may also be reflected in the variation of congener composition, in particular different ratios between mono- and di-rhamnolipids.

Obviously, the molecular structure and the particular mixture of congeners influence physicochemical properties like hydrophobicity or self-assembly behavior of the produced biosurfactant (Nitschke et al. 2005). These are connected to important parameters for potential use for industrial applications including surface tension, critical micelle concentration, foaming behavior, wetting properties, and emulsification activity. Furthermore, biological activity is of interest. In literature, data can be found on these properties for rhamnolipid mixtures showing the high potential of these biosurfactants. However, reliability of this data is often hampered by the use of congener mixtures and impure samples.

Based on the properties reviewed, the focus of this chapter shifts to suitable applications. These include the use of rhamnolipids in diverse field such as bioremediation, agriculture, and enhanced oil recovery as well as in the food, cosmetic, pharmaceutical, and detergent industry. Also biological control benefits from the use of rhamnolipids. Examples include the removal of biofilms. Again, the high amount of published applications shows that the scientific interest in rhamnolipids is high and that this high activity can lead to applications of industrial interest. However, reported applications have to be considered with care; as in most cases, no specific information about the exact composition of the applied rhamnolipids or the purity of the samples is available.

A comprehensive analysis of the patent landscape shows the transfer of scientific knowledge to actual applications. The main applications fields identified previously are also mirrored in the patents. Moreover, it can also be deducted from the patent data that a lot of companies are considering rhamnolipids as viable alternative to petrochemical-derived synthetic surfactants. Fig. 5 shows that the number of patent applications follows the number of published scientific papers with a couple of years behind.
Fig. 5

Number of published scientific papers and patent applications accumulated

Following up on the path taken, further development toward cost competitiveness of production processes and the production of tailored rhamnolipid mixtures with a specific composition adapted to desired physiochemical properties for an ever-increasing field of applications will contribute to the promises of the envisaged bioeconomy.



The Deutsche Bundesstiftung Umwelt (DBU) is gratefully acknowledged for providing financial support.

This work was partially funded by the Cluster of Excellence “Tailor-Made Fuels from Biomass” (TMFB), which is funded by the Excellence Initiative of the German federal and state governments to promote science and research at German universities.

The scientific activities of the Bioeconomy Science Center were financially supported by the Ministry of Innovation, Science, and Research within the framework of the NRW Strategieprojekt BioSC (No. 313/323-400-002 13).

The authors have received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement no. 633962 for the project P4SB.


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Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  • Till Tiso
    • 1
  • Stephan Thies
    • 2
  • Michaela Müller
    • 3
  • Lora Tsvetanova
    • 4
  • Laura Carraresi
    • 4
  • Stefanie Bröring
    • 4
  • Karl-Erich Jaeger
    • 2
    • 5
  • Lars Mathias Blank
    • 1
    Email author
  1. 1.iAMB – Institute of Applied MicrobiologyABBt – Aachen Biology and Biotechnology, RWTH Aachen UniversityAachenGermany
  2. 2.Institut für Molekulare EnzymtechnologieHeinrich-Heine-Universität DüsseldorfJülichGermany
  3. 3.Fraunhofer – Institute for Interfacial Engineering and BiotechnologyStuttgartGermany
  4. 4.Institute for Food and Resource Economics, Chair for Technology and Innovation Management in AgribusinessRheinische Friedrich-Wilhelms-Universität BonnBonnGermany
  5. 5.Institut für Bio- und Geowissenschaften IBG-1: BiotechnologieForschungszentrum Jülich GmbHJülichGermany

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