(330g) Bioremediation Potential of Mixed Culture Microbial Fuel Cell Communities

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            Microbial fuel cells (MFCs) have garnered a large amount of attention partly because of their ability to generate power through the oxidation of several different organic compounds. One aspect of MFC systems currently under investigation is utilizing the reducing potential at the cathode to perform treatment as well. Of more interest is the potential of utilizing the cathode to reduce polluting heavy metals such as uranium or chromium. Oxidized forms of these metals are soluble and highly mobile. Upon reduction, these metals generally form insoluble precipitates, facilitating their immobilization and preventing their exposure to the environment.

            Many studies focus on utilizing model organisms as biocatalysts because of the simplistic nature of the biofilm and well documented electron transfer mechanisms. However, practical application to polluted environments necessitates the use a mixed culture community, if only because of the inability to maintain a pure culture in an open environment.  Enriched multispecies communities may be less susceptible to alteration by introduction of a contaminating species. Mixed microbial communities are more adaptable to changes in substrate type, concentration, and availability.

            In this study, the focus of the MFC systems is aimed at catalyzing the reduction reaction occurring at the cathode. To achieve this, two approaches were utilized. The first approach was the direct enrichment of a microbial community at the cathode exposed to chromium concentration. The second, adapted from previous reports of mixed cathodic communities, requires first the enrichment of a community at the anode of an operating MFC. Once a community has established, the electrode may be switched to reducing conditions and the electrode, once the anode of the MFC, can be utilized as the cathode.

            For these enrichments, major fuel cell community members were identified by 16S rDNA isolated by denaturing gel gradient electrophoresis. These DNA sequences were identified and a phylogenetic tree was constructed to determine the main bacterial groups involved. In this manner, the two different methods of enrichment can be compared. Performance of these enrichments was evaluated based on each community's ability to reduce hexavalent chromium and efficiency in transferring electrons between the cathode and the soluble chromium species.