Potential of willow and its genetically engineered associated bacteria to remediate mixed Cd and toluene contamination
The purpose of this study was to investigate if bacteria with beneficial properties that were isolated from willow growing on a metal-contaminated site can be further equipped with genes coding for a specific degradation pathway to finally obtain transconjugants that can be inoculated in willow to improve phytoremediation efficiency of mixed contaminations.
Materials and methods
Cultivable rhizosphere bacteria and root endophytes were isolated from willow (cv. Tora) growing on a metal-contaminated soil. All isolated strains were tested for their metal resistance and potential to promote plant growth. The two most promising strains were selected and were equipped with the pTOM plasmid coding for toluene degradation. Both transconjugants were inoculated separately and combined in willow cuttings exposed to mixed Cd–toluene contamination, and their effect on phytotoxicity, Cd uptake, and toluene evapotranspiration was evaluated.
Results and discussion
Many of the isolated strains tested positive for the production of siderophores, organic acids, and indole acetic acid (IAA) and showed increased Cd resistance. The Cd-resistant, siderophore-producing rhizosphere strain Burkholderia sp. HU001 and the Cd-resistant root endophyte Pseudomonas sp. HU002, able to produce siderophores, organic acids, and IAA, were selected as receptors for conjugation with the toluene-degrading Burkholderia vietnamiensis BU61 as a donor of the pTOM-TCE plasmid. Although inoculation with the individual transconjugant strains had no effect on plant growth and negatively affected Cd uptake, their combined inoculation resulted in an increased shoot biomass upon Cd–toluene exposure did not affect Cd uptake and strongly reduced evapotranspiration of toluene to the atmosphere.
In this study, inoculation of willow with a consortium of plant-associated bacteria equipped with the appropriate characteristics resulted in an improved phytoremediation of a mixed Cd–toluene contamination: the degradation of toluene was improved leading to a decreased toxicity and evapotranspiration, while Cd uptake and translocation were not affected.
KeywordsCadmium Co contamination Plant-associated bacteria Salix Toluene Willow
This research was funded by the Institute for the Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen) J.D. and by the Fund for Scientific Research Flanders (FWO-Vlaanderen), Ph.D. grant for S.C. and S.T. This work has been financially supported by the UHasselt Methusalem project 08M03VGRJ and by the European Commission under the Seventh Framwork Programme for Research (FP7-KBBE-266124, GREENLAND). S.T. was supported by Laboratory Directed Research and Development funds (LDRD09-005) at the Brookhaven National Laboratory under contract with the U.S. Department of Energy.
- Cunningham J, Kuiack C (1992) Production of citric and oxalic acids and solubilization of calcium phosphate by Penicillium bilaii. Appl Environ Microbiol 58:1451–1458Google Scholar
- Mergeay M, Nies D, Schlegel HG, Gerits J, Charles P, Van Gijsegem F (1985) Alcaligenes eutrophus CH34 is a facultative chemolithotroph with plasmid-bound resistance to heavy metals. J Bacteriol 162:328–334Google Scholar
- Ruttens A, Boulet J, Weyens N, Smeets K, Adriaensen K, Meers E, Van Slycken S, Tack F, Meiresonne L, Thewys T, Witters N, Carleer R, Dupae J, Vangronsveld J (2011) Short rotation coppice culture of willow and poplar as energy crops on metal contaminated agriculture soils. Int J Phytoremediat 13:194–207CrossRefGoogle Scholar
- Said WA, Lewis DA (1991) Quantitative assessment of the effects of metals on microbial degradation of organic chemicals. Appl Environ Microbiol 57:1498–1503Google Scholar
- Shields MS, Reagin MJ (1992) Selection of a Pseudomonas cepacia strain constitutive for the degradation of trichloroethylene. Appl Environ Microbiol 58:3977–3983Google Scholar
- Shields MS, Reagin MJ, Gerger RR, Campbell R, Somerville C (1995) TOM, a new aromatic degradative plasmid from Burkholderia (Pseudomonas) cepacia G4. Appl Environ Microbiol 61(4):1352–1356Google Scholar
- Top E, Van Rollegem P, van der Lelie D, Mergeay M, Verstraete W (1992) The importance of retromobilization to gene dissemination. In: Gauthier MJ (ed) Gene Transfers and Environment. Springer-Verlag Heidelberg, FRG, pp 127–134Google Scholar
- Valls M, de Lorenzo V (2002) Exploiting the genetic and biochemical capacities of bacteria for the remediation of heavy metal pollution. FEMS Microbiol Rev 26:327–338Google Scholar
- van der Lelie D (1998) Biological interactions: the role of soil bacteria in the bioremediation of heavy metal-polluted soils. In: Vangronsveld J, Cunningham SD (eds) Metal-contaminated soils: in situ inactivation and phytorestoration. Springer, Berlin Heidelberg New York, pp 31–50Google Scholar
- Van Ginneken L, Meers E, Guisson R, Ruttens A, Elst K, Tack FMG, Vangronsveld J, Diels L, Dejonghe W (2007) Phytoremediation for heavy metal contaminated soils combined with bioenergy production. J Environ Eng Landsc 15:227–236Google Scholar
- Weyens N, Boulet J, Adriaensen D, Timmermans J-P, Prinsen E, Van Oevelen S, D’Haen J, Smeets K, van der Lelie D, Taghavi S, Vangronsveld J (2012) Contrasting colonization and plant growth promoting capacity between wild type and a gfp-derative of the endophyte Pseudomonas putida W619 in hybrid poplar. Plant Soil 356(1–2):217–230CrossRefGoogle Scholar