Isolation Of Current Producing Bacteria And Their Application In Microbial Fuel Cells

Due to the recent woldwide shortage of fossil energy and significant impacts of global warming which often brings the extreme weather events, readily available biomass has attract much attention as an alternative energy source. Microbial fuel cells (MFCs) are devices that convert chemical energy directly from organic matter in the biomass using electrochemically active bacteria as catalysts to generate electrical energy. Compared to the traditional indirect transformation of energy, this direct conversion from primary fuel to electricity makes it theoretically possible to achieve a higher efficiency. In practice, however, the power output of MFC is still maintained at a comparatively lower level due to many constraints and need further optimization to increase the overall performance of MFCs.By enrichment with lactate as electon donor and electrode as electon accepter in MFCs, five current producing bacteria were isolated from the coastal samples collected in Xiamen. All of the isolated can generate considerable electricity current in MFCs. Sequnce analysis of 16S rRNA and gyrB gene and DNA-DNA hybridization identified strain S1, S5 and EP1 belong to Shewanella decolorationis, Shewanella aquimarina and Shewanella marisflavi, respectively. Using DNA-DNA hybridization, strain S2 and S4 were palced within one species. On the basis of phylogenetic and phenotypic characteristics, S4, choosen as type strain, was classified in the genus Shewanella as a distinct novel species. In addition, using Fe(III) oxide as electron acceptor one hyperthermophile was isolated from hot spring samples.Strain EP1, belonging to Shewanella marisflavi based on polyphasic analysis, which could reduce Fe(III) and generate power at a high ionic strength of up to 1488 mM (8% NaCl) using lactate as the electron donor. Using this bacterium, a measured maximum power density of 3.6 mW/m2 was achieved at an ionic strength of 291 mM. The maximum power density was increased by 167% to 9.6 mW/m2 when ionic strength was increased to 1146 mM. However, further increasing the ionic strength to 1488 mM resulted in a decrease in power density to 5.2 mW/m2. Quantification of the internal resistance distribution revealed that electrolyte resistance was greatly reduced from 1178 to 50 ? when ionic strength increased from 291 to 1488 mM. These results indicate that isolation of specific bacterial strains can effectively improve power generation in some MFC applications.