Better, faster, stronger: Evolving Geobacter species for enhanced capabilities

The bacterial family of Geobacteraceae is comprised of many members including both Geobacter and Pelobacter species. The Geobacteraceae are the predominant Fe(III) reducing organisms in the subsurface due to their capacity for extracellular electron transfer, and play an important role in both the carbon and iron cycles in sedimentary environments. Their metal reducing capabilities can be applied to groundwater bioremediation and to the production of electrical current in microbial fuel cells. Although many members of this family are well known for their novel electron transfer mechanisms, there are also species that are capable of syntrophic growth, coupling the oxidation of certain organics with the production of byproducts, which in turn support the growth of partner microbes. It is a rare occurrence that a pure culture is applied for use in a large-scale bioreactor or in the sediment during in situ bioremediation. That being true, the study of the Geobacteraceae in pure culture and in microbial communities has far reaching significance. Laboratory evolution techniques were used to determine whether Geobacter species could evolve enhanced fitness in novel environments within a laboratory setting, offering insight into how these versatile microbes change with their environments. G. sulfurreducens was adapted for enhanced growth on lactate as a novel carbon and energy source, and the metabolic, regulatory, and genomic changes due to this adaptation were documented. Enhanced growth on lactate could be applied to the bioremediation of harmful metal contaminants by offering a more efficient and cost effective growth substrate relative to the current one used to stimulate the growth of Geobacter species in the subsurface. Laboratory adaptation techniques were also used to determine whether two different Geobacter species could grow together in coculture, and by what mechanisms the two species would interact. This latter study advances the field of interspecies electron transfer, by offering a novel mechanism of electron transfer between microbial cells. This is relevant to the mechanisms that may be used in situ, such as in biofilms, microbial mats, or wastewater granules