Selection of bacteria capable of dissimilatory reduction of Fe(III) from a long-term continuous culture on molasses and their use in a microbial fuel cell.

Ferric ion-respiring microorganisms (FRMs) are a group of prokaryotes that use Fe(III) as well as other metals as terminal electron acceptors in the process of anaerobic respiration. Special attention is paid to a biotechnological significance of FRMs because of their potential role in electricity production in microbial fuel cells (MFCs) where the terminal acceptor of the electrons during anaerobic respiration is not a ferric ion but the anode. One of the best known FRMs is the Shewanellaceae family. Most of the Shewanella species have been isolated from marine environments. In this report, sugar beet molasses and ferric oxide were successfully used in the selection of a bacterial consortium capable of dissimilatory Fe(III) reduction in a long-term continuous culture. The inoculum was a sample of eutrophic lake bottom sediment. Among the bacteria present in this culture were representatives of the Enterobacteriaceae, and the genera Pseudomonas, Arcobacter, and Shewanella. Two non-marine Fe(III)-reducing Shewanella-related clones named POL1 and POL2 were isolated. The abilities of the POL1 and POL2 isolates to metabolize a panel of 190 carbon sources were examined using a BIOLOG assay. The results confirmed the abilities of the shewanellas to utilize a broad range of carbon substrates. The utility of the POL1 and POL2 isolates in H-type MFCs operating on pyruvate or molasses was demonstrated. The operation of the MFC with shewanellas cultured on molasses was shown for the first time. A two-stage character of the fuel cell polarization curves, not previously noted in Shewanella MFC studies, was observed.