| This thesis presents studies that examine microbial extracellular electron transfer that an emphasis characterizing how environmental conditions influence electron flux between microbes and a solid-phase electron donor or acceptor. I used bioelectrochemical systems (BESs), fluorescence and electron microscopy, chemical measurements, 16S rRNA analysis, and qRT-PCR to study these relationships among chemical, physical and biological parameters and processes.;Chapter 1 introduces the concepts of microorganisms, microbial metabolism, extracellular electron transfer, and the value of BESs to provide essential background and motivation for the projects in this thesis.;Chapter 2 presents how variations in the time an anode is connected influences cumulative charge, current and microbial community composition in an environmental BES. When disconnection times are sufficiently short, the current decreases due to an increase in the overall electrode reaction resistance. These results indicate that replenishment of depleted electron donors within the biofilm and surrounding diffusion layer is necessary for maximum electron transfer. Such experiments are valuable in determining performance factors of BESs and in optimizing field-deployed systems.;Chapter 3 aims at demonstrating if an iron-oxidizing photoautotroph can take up electrons from a poised electrode. The subject of this study is Rhodopseudomonas palustris TIE-1, which can oxidize Fe2+ to Fe3+ with light for energy generation. The results indicate TIE-1 can accept electrons from a poised electrode, with carbon dioxide as the sole carbon source/electron donor. Genes encoding for membrane proteins implicated in iron oxidation (the pioABC operon) play a role in electron uptake. This reveals a previously unknown metabolic versatility of photoferrotrophs to use extracellular electron transfer for electron uptake in the presence of light.;Chapter 4 aims at determining if microbial methane production can be stimulated using BESs. This study examines two methanogens, Methanosarcina barkeri Fusaro and Methanosarcina acetivorans C2A, at different electrode potentials. While M. barkeri has hydrogenases with metalloprotein subunits, M. acetivorans does not. A poised electrode stimulates methanogenesis for M. barkeri but not for M. acetivorans, implicating the role of these hydrogenases in microbial extracellular electron transfer. These data demonstrate of the viability of microbial electrosynthesis and indicate how media composition influences net current in BESs. |
