Electromicrobiology and biotechnological applications of the exoelectrogens Geobacter and Shewanella spp.

Electromicrobiology is a sub-discipline of microbiology that investigates electrical interplay between microorganisms and redox active materials, such as electrodes and solid-phase minerals, and the mechanisms underlying microbial ability to exchange electrons with the redox active materials that are external to the microbial cells. The microorganisms with extracellular electron transfer capability are often referred to as exoelectrogens. Although exoelectrogens were documented in early 1900's, discovery of the dissimilatory metal-reducing microorganisms Geobacter and Shewanella spp. in late 1980's marked the beginning of modern electromicrobiology. Since then, thorough and rigorous studies have made Geobacter and Shewanella spp. the two best characterized groups of exoelectrogens. These include identification and characterization of the molecular mechanisms for exchanging electrons with electrodes by Geobacter sulfurreducens and Shewanella oneidensis. In addition, a variety of applications of Geobacter and Shewanella spp. in microbial fuel cells and electrobiosynthesis, such as maintenance of redox balance during fermentations and bioremediations, have also been developed. This review briefly discusses the molecular mechanisms by which G. sulfurreducens and S. oneidensis exchange electrons with electrodes and then focuses on biotechnological applications of Geobacter and Shewanella spp. in microbial fuel cells and electrobiosynthesis as well as the future directions of this research area.