Microbially Influenced Corrosion and its Control Measures: A Critical Review

Corrosion of materials, induced either by chemicals, or environmental factors or microbials is always a threat to industries. If remain unattended, it will have direct influence on environmental pollution. In recent years lot of work is reported on microbially influenced corrosion which is more prevalent in biotechnology and chemical engineering process industries. However, reports for preventive measures which are taken to mitigate microbially induced corrosion are highly limited. This review is an attempt to consolidate and make a systematic, up to date report on various control techniques that could be implemented to overcome microbially influenced corrosion. The review report opens up by highlighting the causes and concerns related to microbially influenced corrosion, and explains in detail mechanistic aspects of it. It provides in-depth view on attenuating microbially influenced corrosion by using synthetic compounds, green inhibitors, surface modifications, biofilm formation, and nano-particles. The review critically discusses the corrosion inhibition mechanism with merits and limitations of each microbially influenced corrosion inhibitors.


Introduction
Corrosion happens spontaneously when alloys and metals attempt to revert to a thermodynamic state with more stability. It could be consequence of chemical attack or interaction of metals with their surroundings. All metals, with the exception of platinum and gold, are found in impure forms in nature, primarily as stable oxides or sulfides, and require processing to convert them into their pure metal form. Most of the methods of extraction involve the use of energy, which leaves the pure metals in a higher energetic state than their ore. The simplest and quickest way to bring metals to their most stable state is therefore through corrosion [1]. However, corrosion poses a threat to the environment and has a negative impact on the economy, environmental protection, and in a variety of engineering applications, including those in the construction of buildings, chemical, automotive, mechatronics, metallurgical, medical, and other fields [2].
The National Association of Corrosion Engineers (NACE) issued an updated statement in which the yearly global expenditure on corrosion was estimated to be around USD 2.5 trillion, comprising nearly 3-4.5% of the GDPs of numerous underdeveloped, developing, and developed countries [3]. By implementing previously developed corrosion protection systems, up to USD 875 billion (35%) to USD 375 billion (15%) can be lowered in economic cost. However, as industrialization and the use of metallic assets grow, the economic expense of corrosion is likely to rise [4]. To prevent and mitigate corrosion decay and lower maintenance costs for metals in corrosive environments, numerous approaches have been used, including corrosion-resistant alloys, corrosion inhibitors, protective coatings, and anodic/ cathodic protection [5].
Microbially influenced corrosion (MIC) is a type of electrochemical process that causes metal surfaces to corrode. It is sparked by harmful microbial metabolic secretions like inorganic and organic acids, ammonia, and sulfides, which have the ability to transfer electrons and perform

MIC and Bacteria
Numerous physiological traits present in the microorganisms are engaged in the MIC of metals like iron, copper, and aluminum as well as their alloys. The metabolic requirements of metal corrosion bacteria for different respiratory substrates or electron acceptors are divided into different classes. When oxygen becomes relatively less in the environment, many bacteria have the ability to substitute other oxidizable substances as terminal electron acceptors in respiration. This enables them to be active in a variety of environments that promote metal corrosion [16].
Among the microorganisms that induce biocorrosion, bacteria are the first to count upon. Due to their smaller size and higher surface-to-volume ratio, bacteria can carry out chemical reactions much more rapidly than larger organisms. Bacterial metabolic activities degrade organic matter into simpler products, which are then used to produce biomass. These metabolic processes change the immediate environment, which leads to the material corroding [17].
Since the 1960s, several bacteria have been linked to the biocorrosion process. According to Beech, the main types of microorganisms responsible for microbiologically influenced corrosion in terrestrial and aquatic habitats include sulfur reducing bacteria (SRB), Iron/manganese oxidizing bacteria, Iron reducing bacteria, sulfur oxidizing bacteria, and bacteria that produce organic acids and slimes [13,18,19].
Lactobacillus, Acetobacter, Azospirillum, and Azotobacter are examples of microbes that metabolize to secrete organic and inorganic acids (lactic, acetic, and formic acids) and influence the corrosion process [20]. In the gram-negative category, sulfate-reducing bacteria are Desulfovibrio vulgaris of the Desulfovibrionaceae family. These can cause corrosion by interfering with the passivation of the oxide layer on stainless steel. Increased corrosion is the outcome of biofilms on metal surfaces, which open up novel electrochemical reaction pathways or processes that would not be feasible in the absence of microorganisms. In addition, the interfacial interactions between the biofilm and metallic sublayer can be significantly altered by the metabolic by products of bacteria [21]. MIC is a complex process and several mechanisms have been proposed for the same. In literature single consensus on mechanistic aspects of MIC is not found. Most of the researchers suggests chemical microbiologically influenced corrosion, electrochemical microbiologically influenced corrosion (CMIC/EMIC) and biocatalytic cathodic sulfate reduction (BCSR) as possible mechanisms for MIC. Sessile cells in a biofilm can attach iron as an electron donor, in the absence of another electron donor. In anoxic environments, oxidizing agent such as sulfate or nitrate act as electron donor. It is anticipated that, reduction of the electron acceptor takes place inside the cell, the oxidation of the electron donor happens outside the cell. In other words, extracellular electron from outside must enter the cell. This electron transport across the cell wall is called extracellular electron transfer (EET), and the overall mechanism through which the associated corrosion of metal is achieved is called electric microbiologically influenced 221 corrosion (EMIC). The biocatalytic cathodic sulfate reduction (BCSR) is a more generalized theory based on the capacity of SRB and other microorganisms to take energy by extracellular electron transfer (EET) mechanisms.
The microbes respire on an exogenous oxidant such as sulfate and nitrate in their cytoplasm using extracellular electrons. To use the extracellular electrons for the oxidation of an oxidant such as sulfate in the cytoplasm, the electrons must be transported across the cell wall. This kind of extracellular electron transfer (EET) is a feat that is achieved only by electrogenic biofilms. There are two primary methods for EET. One is the direct electron transfer (DET) and the other mediated electron transfer (MET).
Aerobic or facultative populations such as Enterobacteriaceae, Pseudomonadaceae, Bacillaceae, and, Micrococcaceae in addition to SRB, significantly contribute to MIC by forming a slimy biofilm that intensifies corrosion. Iron oxidizing bacteria (IOB) like Gallionella, Siderocapsa, Hyphomicrobium, and Sphaerotilus convert ferrous iron to ferric iron and aid in the formation of iron hydroxides. Microbes such as Pseudomonas and Shewanella reduce iron and manganese oxide to the point where they disable the passive coating on the metal surface, causing a reduction in electron stability and a high corrosion rate [22].

MIC Affecting Various Industries
Concrete structure MIC is a common occurrence in sewer networks. As per statistical data, between 10 and 20% of Germany's damaged concrete infrastructures have sewage structures that are corroded by microbes. As a result, its yearly maintenance costs exceed 450 million euros in Germany, 85 million pounds in the United Kingdom, and 390 billion in the United States between 2002 and 2022 to restore infrastructure the compromised [23]. Figure 2 illustrates the various industries which are affected by MIC.
The formation of biofilm on industrial equipment can impact the flow of water and heat transmission and cause serious corrosion. The bulk of MIC is accountable for pitting corrosion, which causes metal materials to become permeable to pinholes. Microbes are responsible for 20% of corrosion occurring worldwide [24].
Microbes initiating or accelerating a corrosion reaction on a metallic surface is a common problem in the gas [25], oil [26], and shipping industries [27]. It costs various industries money in terms of operational and maintenance costs [28]. MIC activities may cause up to 20% of total annual corrosion damage in the oil and gas industry [29].
In oil and gas installations including pipelines, production lines, cooling circuits, and storage tanks, biofouling has a number of negative effects, one of which is biocorrosion. It can be particularly problematic in submerged pipes and storage tanks where it may potentially pollute the environment. It has an irreversible negative impact on the intrinsic properties of materials [30]. Many other industrial sectors have experienced the impact and severity of MIC, including nuclear power plants, fuel recycle units, power plants, sewage drainage channels, storage vessels, and related areas such as pumps, valves, and vessels, oil

Mechanism Of MIC Inhibition
Microbially influenced corrosion inhibition (MICI) has the following possible mechanisms: (1) Growth inhibition of corrosion-causing bacteria, for example, through antimicrobial production. (2) Removal of corrosive elements that react with the metal surface, such as oxygen consumption through aerobic respiration. (3) Formation of a protective layer, e.g., through an excess of Extracellular Polymeric Substances (EPS). (4) A combination of various mechanisms cab be anticipated in multispecies biofilms [32].
An MIC inhibitor can help deter corrosion possibly by following ways.
(1) By interacting with the corrosive material, the corrosion inhibitor can convert a corrosive environment into a non-corrosive one. (2) With a shielding effect, the corrosion inhibitor can adhere to the metal surface and keep it from corroding. (3) As a biocide, the corrosion inhibitor can instantly destroy bacterial cells upon contact. (4) Plants extracts when used as inhibitors, can improve the film formation on the metal surface with the presence of tannins, cellulose, and polycyclic chemicals in it [33]. (5) Biofilm: Role of biofilm formation in microbially influenced corrosion is reported by many researchers. Microbes may change the electrochemical reaction at the biofilm/metal interface and either inhibit or accelerate the process of metal corrosion. Once a biofilm is formed on a surface, it is difficult to inhibit and/or eradicate it by normal antimicrobial agents. The presence of a biofilm reported to promote the precipitation of protective Zn(OH) 2 on the surface of the material, which inhibited dezincification.
Regardless of whether adequate environmental conditions exist, any microbial activity that either directly or indirectly counters these effects may inhibit the corrosion process [34]. Due to their antibacterial action against microbes, which is determined by characteristics like shape, size, and functional groups, nanomaterials have the ability to prevent biocorrosion. By functioning as a passive film to prevent bacterial attachment and imparting the coating antibacterial activity, nanomaterials can inhibit bacterial growth. It was found that nanoparticles could affect how quickly bacteria adhere to one another and form biofilms [35]. Mechanism of MICI by various inhibitors is illustrated in Fig. 3.
The traditional standards used to choose an efficient biocide include: • efficacy against a variety of microorganisms • the capacity to penetrate and spread microbial slime • compatibility with the environment • secure, simple use and easy storage • suitable biodegradability • cost-effectiveness [36].
Based on above criteria different classes of inhibiting agents are used to mitigate microbially influenced corrosion. They are summarized in Fig. 4

MICI Using Plant Extract
Adopting suitable management and preventive measures can help to control or avoid biocorrosion. Fundamentally, the goal of this prevention and control is largely to destroy microbial cells, with or without preventing the development of biofilms. Corrosion inhibitor usage is considered to be the most efficient of these remedies [37].
Even though several chemical corrosion inhibitors and synthetic biocides have shown anticorrosion abilities, the bulk of them are still very expensive, toxic, and difficult to degrade, posing a serious threat to both animal and human life as well as the environment. Toxicity may arise either during preparation or during applications. In addition to this there is always a threat to environment. Safety of human health and safeguarding the environment is of utmost importance. Strict environmental regulation is imposed on the use of toxic chemicals. Due to these restrictions, scientists are Fig. 3 Illustration role of mechanism of MICI seeking for new classes of biocides and corrosion inhibitors for diverse corrosion systems that are biodegradable, non-toxic, more effective, and ecologically acceptable [37]. Non-toxic, biodegradable plants are currently being gathered to produce natural chemicals that can be utilized as green corrosion inhibitors and biocides. Using naturally occurring substances, such as plant extracts, to treat MIC is regarded to be environmentally friendly. Many plant oils and aqueous plant extracts have been shown to have an inhibitory effect on yeast, bacteria, and filamentous fungus [38]- [41].
The ability of Phyllanthus amarus to prevent the corrosion of carbon steel by acid-producing bacteria was investigated using the weight loss technique in both the presence and absence of aqueous crude extract. According to the phytochemicals found in the aqueous extract, Phyllanthus amarus has a high concentration of tannins, alkaloids, and phenolic compounds, demonstrating its bio-potency and antibacterial characteristics [42].
According to most reports, chemical corrosion rates rise as temperature rises. However, a study observed no increase in corrosion rate with rising temperature, with the exception of the extract + D-tyrosine mixture. The observed difference is most likely caused by the temperature limiting the operations of microorganisms. Mesophilic microorganisms like our SRB isolates cannot grow or function properly at temperatures higher than 40 °C [43]. Table 1 presents various plant extracts applied for inhibition of MICI.

MICI Using Surfactants
Surfactants are another well-liked antibacterial substance that can be manufactured both synthetically and biologically. Specific bacteria, fungi, and yeasts produce biosurfactants, which are secondary metabolites and surface-active amphiphilic chemicals of biological origin. The most prevalent of these are Bacillus subtilis, Pseudomonas aeruginosa, Candida albicans, and Acinetobacter calcoaceticus [44].
Surfactant molecules' distinctive properties highlight their adaptability in emulsifying, wetting, dispersing, solubilizing, and decontaminating. The amphiphilic properties of surfactant molecules establish an affinity between the metal surface and corrosive liquid during the stimulation of an oil and gas reservoir. Surface tension arises when molecules are in contact with cohesive energy. Van der Waals interactions and hydrogen bonding between the water molecules are present in watery media. Hydrogen bonding is, however, insufficient above the air-water barrier. Van der Waals interactions at this interface are additionally weakened by the absence of interacting molecules in the air phase. Therefore, compared to molecules in the bulk phase, molecules at the air-water interface have greater accessible energy and fewer chances  Acid producing bacteria [42] for bonding. The hydrophobic component of surfactant molecules tries to travel to accessible interfaces in aqueous systems in order to avoid the undesired polar solvent. Surface tension is reduced by adsorption of surfactant molecules at the air-water interface. Surfactant molecules become more active at the air-water interface as a result [45]. The tendency for physical adsorption and aggregation increases as the surfactant molecules increase, and the associated adsorption is evidenced by decreasing surface tension [46]. Surfactants can also significantly escalate the dispersion of crude oil in water, lower the interfacial tension between oil and water, and alter the wettability of metal surfaces. The hydrophobic chain can also be placed on the metal surface in a particular pattern to produce a hydrophobic film that stifles the cathode reaction by preventing water molecules from diffusing into the cathode area. The level of adsorption and corrosion inhibition is determined by the surfactant's properties and interactions with metal and the surrounding environments [47].
Depending on their chemical make-up and origin from microorganisms, these have been divided into five major classes: phospholipids, lipopeptides, glycolipids, polymeric compounds, and neutral lipids. The biosurfactant functional group's adsorption onto the metal surface is the most crucial measure in the process of inhibiting corrosion. The capacity of biosurfactants for adsorption is correlated with their capacity to agglomerate to form micelles and establish a protective layer at the metal surface [48].
SRB bacteria are effectively fought off by cationic surfactants. Cationic surfactants are drawn to the phospholipid bilayer that makes up the cytoplasmic membrane, which also includes proteins. The exterior surface of the bacterial cell wall, which has a negative charge, is where the cationic antimicrobial surfactants engage and get adsorbed. The surfactant molecules enter the cell membrane as a consequence of this adsorption, causing cell damage. The negative charges on membranes are counterbalanced by the positive charges on cationic molecules, allowing them to flow inside the cytoplasmic membrane. The outcome is a total deactivation of the selective permeability that distinguishes the outer cell membrane. Such interaction stops growth, which is enough to decrease the fluidity of the membrane and eventually cause cell death [7].
The adsorption theory in conjunction with the bactericidal effect can be used to explain the inhibition mechanism. The cationic group of quaternary ammonium salt is thought to adsorb onto the negatively charged SRB biofilm surface. Hydrophobic alkyl chain of quaternary ammonium salt is thought to penetrate into the cellular membrane. These processes will modify the biological functions of the cell membrane, such as electron transfer, isolation barrier, selective material transfer, and so on. This will result in destroy of the selective permeability and genetic system of the cell membrane, inhibiting the cell membrane's selective permeability and genetic system.
Bacillus subtilis A1, Streptomyces, parvus B7, Pseudomonas stutzeri NA3, and Acinetobacter baumannii MN3 are the bacterial strains which showed a reduced metal degradation in the presence of glycolipid type of biosurfactant used as a microbial inhibitor for corrosion of bacterial strains. The inhibition efficiency was found about 87% for mixed consortia included with biosurfactant system. In other words, glycolipid biosurfactant as an eco-friendly microbial inhibitor for the corrosion of carbon steel in vulnerable corrosive bacterial strains.

MICI by Surface Modification
A growing number of metalloid materials, including titanium, gold, silver, zinc, chromium, nickel, cobalt, mercury, copper, have been used as actively microbic surfaces [49]. The antibacterial property depends on the surface-emitted germs keeping them from coming into direct touch with the outside of the biomaterial. On the other hand, researchers have been working to create a modified biomaterial surface that is antimicrobial by either killing microorganisms when they adhere to the surface or stopping their growth [50] [51].

Copper Corrosion and Inhibition
Copper has long been used as a disinfectant by applying coating on the surface of other metals. Its efficacy against microorganisms is dependent on the release of Cu + and Cu 2+ near the copper surface. 2205 duplex stainless steel (2205-Cu DSS), a novel alloy has been created to fight against microbial corrosion. It has copper rich phase which precipitate after being exposed to solutions and aging processes. According to studies done in an aerobic environment, microbiological corrosion on stainless steel due to Escherichia coli, P. aeruginosa, and Staphylococcus aureus were inhibited due to release of copper ions. This fact was indicated by delayed antimicrobial effect [52]. The biocorrosion behavior of Bacillus thuringiensis EN2 and B. oleronius EN9 on copper metal CW024A in cooling water system (1% chloride) were evaluated. In presence of EN2 and EN9, the corrosion rates (CR) were higher, about 0 than control system. On the other hand, the presence of corrosion inhibitor 2-mercaptopyridine (2-MCP) with bacteria (EN2 and EN9), the biofilm on metal surface was highly inhibited and decreased corrosion rate.

Superhydrophobic Coating
As a result of their self-cleaning, anti-fouling, anti-corrosion, and anti-icing qualities, superhydrophobic surfaces are becoming more and more common in a range of applications.
When rough surface microstructures are combined with lowsurface-energy materials, superhydrophobic surfaces with water contact angles more than 150° and slide angles less than 10° are typically produced [53]. When these surface microstructures are exposed to water, an air film can form inside them, functioning as an additional barricade for the substrate materials. In terms of potential coating materials with improved anti-corrosion performance, this characteristic makes superhydrophobic surfaces particularly appealing. However, physical impacts and scratches can harm the delicate microstructures necessary for super-hydrophobicity, which frequently results in a reduction in hydrophobicity and the loss of the additional barrier effect [54].
Few researchers have performed the scratch test to illustrate the surface morphology change due to impacts and scratches. Studies are conducted to illustrate the mechanism of delamination and scratch damages (Molero, et ol.,2019) These coatings have excellent moisture and corrosive ion barriers when they are in good condition. However, the barrier performance of the coatings may be severely jeopardized due to the harm caused by mechanical and environmental assaults during transit and service. Localized scratches, delamination, or stress-related macrocracks can all be signs of damage. The overall protective and cosmetic qualities of coatings may deteriorate more macroscopically as a result of bond breakdown brought on by environmental elements as heat, UV, oxygen, ions, and moisture. If not promptly and efficiently treated, these defects eventually lead to premature coating failures by acting as conduits for the rapid intake of corrosive media. The majority of damaged coatings currently need expensive and time-consuming artificial repairs or replacements. Emerging smart materials technology has the potential to dramatically increase anti-corrosion performance and service life by giving coatings self-healing characteristics [55].
Superhydrophobic coating on copper, which was obtained by laser processing and chemical vapor deposition of fluoro oxisilanes, the bactericidal activity was used to study corrosion processes and the degradation of superhydrophobic state in different biological liquids. It was shown that by controlling the corrosion resistance and the wettability of the superhydrophobic copper substrate, bactericidal action of copper substrates could be sustained for a long time, with simultaneous control over corrosive degradation and release of copper ions in the environment.
The failure of organic coatings in the marine environment is often caused by microbiologically influenced corrosion. This study assembled multilayer antibacterial hybrids onto NaOH etched basalt scales via mussel-inspired depositions of PDA and AgNPs followed by post-modification with 1-Dodecanethiol. 1-Dodecanethiol could suppress the formation of mature biofilms and maintain bacteria in dispersed states, which further promotes the bacterial-killing effect of AgNPs. Meanwhile, 1-Dodecanethiol slowed down the release rate of Ag ions so that an utterly dead biofilm would not be formed on the surfaces of the coatings.
Near-superhydrophobic D-cys/Ag@ZIF-8 (DAZ-8) coatings were fabricated to effectively inhibit the corrosion of X70 carbon steels in simulated seawater. The addition of 0.5 mg/cm 2 DAZ-8 coating reduced the corrosion current density by 90.5% in the presence of Escherichia coli compared with the untreated coupons. Moreover, DAZ-8 also exhibited excellent antibacterial and antibiofouling performance which makes DAZ-8 suitable for MIC inhibition. Different nanomaterials, including metal and metal oxide nanoparticles (NPs), carbon nanostructures and other nonmetallic biocides have demonstrated strong antimicrobial activities and have been used as alternative biocides against MIC.
An environmentally benign approach to surface modification was developed to impart copper surface with enhanced resistance to corrosion, bacterial adhesion and biocorrosion. Oxidative graft polymerization of 2,2′-bithiophene from the copper surface with self-assembled 2,2′-bithiophene monolayer, and subsequent reduction of silver ions to silver nanoparticles (Ag NPs) on the surface, gave homogeneous bithiophene polymer (PBT) film with densely coupled Ag NPs on the copper surface (Cu-g-PBT-Ag NP surface). The immobilized Ag NPs were found to significantly inhibit bacterial adhesion and enhance the antibacterial properties of the PBT modified copper surface. Compared with other composite coatings, Ni-P-Cr/TiO2 nanocomposite coating with its better passive film and unique antibacterial activity caused by TiO2 nanoparticles incorporated, displayed excellent antibacterial and corrosion resistance property, against microbially influenced corrosion. Different types of coating which are applied on metals for MICI is given in Table 2

Self-Healing Based on Defect-Filling Effect
According to this method, mechanical damage causes coating flaws that spontaneously result in the release of the components that can be polymerized to repair wounds. These substances can polymerize into a layer of a certain strength and thickness to repair the coating flaw and restore the coating's barrier properties by interacting with either coexisting catalysts in the coating or with moisture or oxygen in the environment. The healant needs to be sufficiently enclosed in order to increase these components' reactivity and decrease their interaction with the bulk coating ingredients [55].
Most traditional Superhydrophilic and Underwater Superoleophobic (SUS) coatings are typically undesirable in seawater, which is primarily due to coating absorption or mechanical stress on their surface [56,57]. To address the shortcomings of SUS coatings, superhydrophobic surfaces (SHS) have received considerable attention due to their unique barrier blocking on water and corrosive medium [58].

Anti-Protein Coating
Non-bactericidal anti-biofouling surfaces prevent microbial attachment when the physicochemical properties or surface topography are unfavorable to the bacteria [59]. Biofouling and rapid corrosion of metallic objects are two severe problems that can arise when microorganisms build up on the surfaces of materials in an aqueous environment. Protein adsorption is important in the biofouling process, and polymers with anti-protein adsorption properties have received a lot of attention. In recent years, the anti-protein adsorption properties of numerous hydrophobic, hydrophilic, and amphiphilic materials have been studied. The general consensus is that materials made of hydrophilic substances like poly (ethylene glycol) (PEG), oligo (ethylene glycol) (OEG), can create a layer of hydrated film that effectively prevents microorganisms from adhering to surfaces [60].

Coating Using Synthetic Materials
Chemical inhibitors are essential for protecting against corrosion and implementing mitigation measures. Organic compounds with p bonds, heteroatoms (N, S, P, and O), and inorganic compounds such as chromate, nitrite, dichromate, and others are the most effective and efficient corrosion inhibitors. The use of these substances, however, has recently come under scrutiny because of the numerous harms they have done to the environment [61].
Due to its capacity to stop corrosion at very low levels in a highly acidic environment, as well as their minimal toxic effects and broad biological and pharmacological activities, imidazole derivatives have been thoroughly researched as prospective corrosion inhibitors. Imidazole compounds have an inhibitory impact because of the dissociated electron pairs and electrons in their chemical structures [62].

MICI by Bacteria
Microorganisms can minimize corrosion in some circumstances by using one of the two broad mechanisms, or a combination of them: (1) Reducing the environment's exposure to corrosive chemicals and their caustic effects. (2) Creating protective layers on the metal surface or maintaining pre-existing protective coatings [33]. Bacterial exopolymers have been shown to both enhance and hinder corrosion. During non-growing conditions, Pseudomonas S9 is known to produce an exopolysaccharide. When added to the bulk solution of S. marcescens cells or applied to the metal surface prior to the experiment, cell-free Pseudomonas S9-polysaccharide had no effect on corrosion. S. marcescens corrosion was unaffected by Pseudomonas S9 cells, which should have produced polymer when suspended in Nine Salt Solution (NSS) [63].
Organic polymers are commercially used as binding agents in anti-corrosion paints. The metal-in-solution process may be inhibited by a bacterial film, which acts as an organic material barrier against the diffusion of corrosion products. According to Thomas et al. [64], the presence of an organic film acts as a diffusion barrier, preventing hydrogen ions from penetrating the metal lattice and reducing steel's susceptibility to brittleness in seawater. It is possible to talk about corrosion inhibition in terms of bacterial activity and metabolism in general. Experiments show that living bacteria are needed to protect the metal, but they are not necessarily required to grow and divide [65].
Researchers hypothesized that nitrates would outcompete SRB for biodegradable oil organics, promoting the development of nitrate-reducing bacteria (NRB) and preventing corrosion. The production of hydrogen sulfide by SRB can be effectively stopped and inhibited by injecting nitrate into oil fields. 2021) [66].

MICI by Biofilm
Biofilms form when microorganism cells stick together and frequently attach to surfaces. These adherent cells frequently Marine Organic-Inorganic hybrid SUS membrane [56] consist of an EPS matrix that they have produced on their own. To put it another way, microbes on surfaces produce polymers and create gel matrices of bacterial exopolymers that are crucial to the structural integrity of biofilms. The creation of extracellular substances like polysaccharides and proteins results in the formation of these films. The life of the organisms that make up biofilms depends on them in a number of crucial ways for microbial colonization of surfaces [17]. One of the most common methods used by microorganisms to survive is the development of biofilms, which give bacterial species the ability to create their own environments for defense, nutrition, and metabolic interactions. Typically, microbial colonization starts with a single cell attaching to a surface covered in a substance known as a conditioning film [67].
In the following ways, natural symbiotic biofilms are regarded as being superior to traditional corrosion protection techniques: (1) Symbiotic organisms found in corrosionprotective biofilms make them fully non-toxic and environmentally beneficial as compared to chemically cross-linked coatings. (2) Corrosive substances (such as Cl) are prevented from entering by the outer layer of EPS-secreting biofilms, which serves as a physical barrier. (3) Enzymes and secondary metabolites can be secreted to prevent corrosion on steel surfaces. (4) The biofilms may even interact with inorganic materials to produce a mineralized layer that will preserve the metal for a long time [68]. On a metal surface, the development of a biofilm could eliminate the passive film or hinder its recovery [69].
The techniques for preventing biofilm corrosion that are most commonly suggested are as follows: (i) The biofilm prevents metal disintegration by serving as a diffusion barrier for corrosion agents. (ii) The oxygen content at the metal surface is decreased by aerobic bacteria within the biofilm. (iii) Bacteria provide metabolic byproducts that prevent rusting (for example, siderophores) [14].
Bacterial respiration of oxygen assists the reduction in corrosion. Microbiological process other than oxygen depletion, such as the excretion of a metabolic product, was found to be responsible for inhibiting corrosion. Although mechanism of inhibition is not clearly understood, it has been proved that live bacteria are required in the biofilm to maintain the observed corrosion inhibition.
A novel method of controlling biocorrosion has be proposed which involves the use of protective strains of bacteria. Some of these strains seem to be capable of secreting both antimicrobial and corrosion inhibiting compounds. This probiotic approach, called corrosion control using regenerative biofilms (CCURB), has been successfully implemented so far in both laboratory experiments and field tests resulting in two-fold or greater reductions in corrosion rate.
Genetically constructed Bacillus subtilis biofilms secreting antimicrobials indolicidin, bactenecin, and probactenecin were able to inhibit the growth of corrosion-causing SRB (Desulfovibrio vulgaris and D. gigas) and reduce corrosion rates significantly in continuous culture condition. This was the first observation on in situ application of beneficial, genetically engineered antimicrobial-expressing biofilms for corrosion inhibition.
Although the ability of biofilms to reduce or prevent corrosion of steel, copper or aluminum has been recently demonstrated, the use of biofilms to prevent or reduce corrosion of other metals has not yet been investigated.

MICI Using Essential Oils
Essential oils (EOs), also called volatile oils, etherolea, and ethereal oils are plant-derived hydrophobic liquid concentrates. EOs typically retain the essence of the materials from which they were made. Due to their biocompatibility with nature, these oils are also known as eco-friendly inhibitors or green inhibitors. EOs are very appealing for large-scale applications due to their potent anticorrosion, antibacterial, biodegradable, and widely accessibility. However, studies of the effectiveness of EOs in inhibiting MIC are scarce in the literature [70]. Once EOs are generally recognized as safe (GRAS), adding small amounts of other natural preservatives to reinforce their natural antimicrobial effects may be a way to achieve a balance between sensory acceptability and antimicrobial efficiency [71]. Low-dose EO has been reported as a potential means of controlling pathogen and spoilage microorganism growth [72].

MICI Using Nanomaterials
Small bubbles, also known as micro/nano bubbles, are referred to as fine bubbles and have diameters between 10 and 0.1 nm [73]. Nanobubbles are used for many engineering, environmental, biological, and medical applications, and many beneficial results have been reported. Although these benefits sometimes outweigh uncertain scientific reasoning why nanobubbles behave and provide benefits as they do, we need to make sure that basic scientific understanding is the driving force for a continued progress for the research. By increasing the slip length, the surface nanobubbles can act as surface coating material to prevent corrosion initiation [74]. Nanoparticles with anticorrosion and antibacterial properties may be used as coating materials to minimize MIC by reducing bacterial attachment to metal and contact with it [75]. List of various nanoparticles used for MICI is given in Table 3.

MICI Using Ozone
Ozone's effectiveness and lack of harmful product deposition have drawn a lot of attention in recent years. At practical and safe concentrations, ozone rapidly damages bacterial cell walls and is more efficient than chlorine against plant pathogens and animal parasites with thick-walled spores. It has been employed in industries like cooling water systems. When it comes to environmental issues, using ozone has many benefits over using traditional biocides. Ozone is a highly potential biocide for the future due to its highly toxic nature and non-toxic byproduct discharge [77].
In view of such restrictions ozone treatment provides an attractive alternative to the use of other compounds. With extremely high oxidative power, ozone extremely elective against the majority of bacteria present in industrial systems, including microbial biofilms. It is regenerated in the system easily. It has low degree of aggression toward the majority of structural metals inclusive of steel, which is important from the corrosion point of view. Ozone offers several advantages with respect to other biocides. It is non-toxic and its rapid decomposition minimizes downstream toxicity risks, reduction of water discharge. Thus, the combination of high toxicity during treatment with no toxicant discharge could make ozone the biocide of choice for cooling water treatment if the economy is properly monitored.
Cooling water treatment requires effective, environmentally safe biocides compatible with system operation. The unique combination of high biocidal activity during use with no toxic discharge, could render dissolved ozone a safe biocide for cooling water treatment. Planktonic and sessile cells which are frequent microbial contaminant of industrial systems were reported to be used assess the biocidal efficacy of ozone.

Conclusion and Future Recommendations
MIC has a severe impact on industry integrity and is extremely destructive to the vast majority of building frameworks. Different types of corrosion destruction are brought by it, increasing operating and maintenance expenses thereby interfering with productivity. This review discusses the different methods used by industries to mitigate MIC. MIC can be brought down by various techniques. Surface modification, the use of various coating agents such as plant extracts, surfactants, bacteria, biofilm, essential oils, nanomaterials, ozone and biomass derived materials are the major ones. Industries are battling MIC with these wide range of tactics however, more study and development needs to be done to effectively inhibit it. In all the reported literatures, not much is reported about the mechanistic aspects. By considering individual type of MIC inhibitors in depth studies can be done to elaborate upon mechanism. Further there is wide scope to introduce new class if MIC inhibitors such as biopolymers and ionic liquids. Research can also be explored for the utility of quantum dots for effective control technique. Thus, utilizing modern technologies to aid in MIC anticipation and control can assist find and fix a variety of problems.
Author contributions Dr LM: Conceptualisation, validation of literature; manuscript writing& editing. Dr PR: Literature update, manuscript writing & editing.
Funding Open access funding provided by Manipal Academy of Higher Education, Manipal.
Data availability Data can be accessed form corresponding author upon request.

Conflict of interest
The authors declare that they have no competing interests. On behalf of authors, corresponding authors claims no conflict of interest.
Ethical approval Applicable for both human and/ or animal studies. Ethical committees, Internal Review Boards and guidelines followed must be named. When applicable, additional headings with statements on consent to participate and consent to publish are also required. Not applicable.
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