Electricity generation by thermophilic microorganisms from marine sediment

The search for microorganisms that are capable of catalyzing the reduction of an electrode within a fuel cell has primarily been focused on bacteria that operate mesobiotically. Bacteria that function optimally under extreme conditions are beginning to be examined because they may serve as more effective catalysts (higher activity, greater stability, longer life, capable of utilizing a broader range of fuels) in microbial fuel cells. An examination of marine sediment from temperate waters (Charleston, SC) proved to be a good source of thermophilic electrode-reducing bacteria. Electric current normalized to the surface area of graphite electrodes was approximately ten times greater when sediment fuel cells were incubated at 60°C (209 to 254 mA/m²) vs 22°C (10 to 22 mA/m²). Electricity-generating communities were selected in sediment fuel cells and then maintained without sediment or synthetic electron-carrying mediators in single-chambered fuel cells. Current was generated when cellulose or acetate was added as a substrate to the cells. The 16S ribosomal ribonucleic acid genes from the heavy biofilms that formed on the graphite anodes of acetate-fed fuel cells were cloned and sequenced. The preponderance of the clones (54 of 80) was most related to a Gram-positive thermophile, Thermincola carboxydophila (99% similarity). The remainder of clones from the community was most related to T. carboxydophila, or uncultured Firmicutes and Deferribacteres. Overall, the data indicate that temperate aquatic sediments are a good source of thermophilic electrode-reducing bacteria.