Plasmid transfer in biofilms: integrating fundamental and applied research

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The overall objective for the proposed research program is to elucidate the complex interactions of biofilms with their environment and the effect of these interactions on catabolic plasmid transfer, maintenance, dissemination and consequent contaminant biodegradation. To initially focus the project scope, subsurface-derived biofilms will be investigated. The knowledge generated by the proposed research will be crucial not only for the assessment of the success of natural attenuation and biodegradation in the subsurface but can be applied to other environments, such as benthic communities, drinking water biofilms, intestinal biofilms or biofilm reactors. The exchange of genetic information between cells is a common phenomenon in both natural and engineered environments and may significantly contribute to accelerated adjustment of microbial communities. Biofilms, accumulations of microorganisms and extracellular polymeric substances, represent environmental niches characterized by high cell densities and thus provide ideal environments for gene transfer to occur. Catabolic genes or those coding for antibiotic or metal resistance are often carried on plasmids. Plasmid transfer via conjugation (the exchange of genetic information from one cell to another mediated by cell to cell contact) can be viewed as a bioaugmentation strategy and has been shown to contribute to the spread of catabolic genes in various ecosystems. Despite the fact that plasmid transfer is known to play a critical role in biofilms, little is known about the exact way in which the surrounding environment influences conjugation frequencies and fate of plasmids in biofilms. The proposed work will test the hypothesis that subsurface biofilms facilitate plasmid transfer and consequently contribute to an increased biodegradation potential in aquifers by conducting a very careful set of experiments in continuous flow-through chambers and lab scale microcosms simulating "real world" conditions using well characterized catabolic plasmids. The findings from the proposed work will span a bridge to clinical and public health microbiology (spread of antibiotic resistance plasmids in biofilms) and bioremediation strategies.