| Microbial fuel cells are batteries in which microorganisms catalyze the conversion of organic fuel (such as lactate) into protons and electrons that power a resistor (e. g., a light bulb) before reducing the terminal electron acceptor (e. g., oxygen is reduced to water). Great improvements in power production and efficiency have been made by engineering inorganic components, such as the electrodes themselves, to be more efficiently utilized by fuel cell-inhabiting organisms. However, other avenues for improvement may exist, that is, engineering the fuel cell-inhabiting organisms themselves. We hypothesized that Shewanella oneidensis MR-1, a model organism used for studying microbial fuel cells, could be shown to evolve under physiological conditions which mimic those found in microbial fuel cells. These physiological conditions include the planktonic lifestyle, the biofilm lifestyle, and transient association between the two—that is, those cells that rapidly detach from and reattach to the biofilm.;Here we show the Growth Advantage in Stationary Phase (GASP) phenotype conferred by aging cells planktonically in conditions of abundant electron donor and acceptor, as well as conditions of either electron donor or acceptor limitation. In general, the longer cells are aged planktonically, the greater their advantage when competing in a similar environment. A GASP-like phenotype is also conferred by aging cells in a biofilm for 10 days, though aging cells continuously within a biofilm for 20 days resulted in a competitive disadvantage. To better understand cells that are transiently associated with both lifestyles, we observed the rapid formation of, detachment from and reattachment to biofilms. Biofilm spontaneously form both where oxygen is plentiful and where it is scarce. Oxygen-replete biofilms and oxygen-poor biofilms respond to different supplementary amino acids. Response to amino acid supplementation also varies according to the developmental stage of these biofilms. These data may offer insight into the biology of microbial fuel cells, as well as guidance for physiological treatments and methods of directed evolution that will improve microbial fuel cell performance. |
