Yi H, Nevin KP, Kim B-C, Franks AE, Klimes A, Tender LM et al.. Selection of a variant of Geobacter sulfurreducens with enhanced capacity for current production in microbial fuel cells. Biosens Bioelectron 24: 3498-3503
Geobacter sulfurreducens produces current densities in microbial fuel cells that are among the highest known for pure cultures. The possibility of adapting this organism to produce even higher current densities was evaluated. A system in which a graphite anode was poised at -400 mV (versus Ag/AgCl) was inoculated with the wild-type strain of G. sulfurreducens, strain DL-1. An isolate, designated strain KN400, was recovered from the biofilm after 5 months of growth on the electrode. KN400 was much more effective in current production than strain DL-1. This was apparent with anodes poised at -400 mV, as well as in systems run in true fuel cell mode. KN400 had current (7.6A/m(2)) and power (3.9 W/m(2)) densities that respectively were substantially higher than those of DL1 (1.4A/m(2) and 0.5 W/m(2)). On a per cell basis KN400 was more effective in current production than DL1, requiring thinner biofilms to make equivalent current. The enhanced capacity for current production in KN400 was associated with a greater abundance of electrically conductive microbial nanowires than DL1 and lower internal resistance (0.015 versus 0.130 Omega/m(2)) and mass transfer limitation in KN400 fuel cells. KN400 produced flagella, whereas DL1 does not. Surprisingly, KN400 had much less outer-surface c-type cytochromes than DL1. KN400 also had a greater propensity to form biofilms on glass or graphite than DL1, even when growing with the soluble electron acceptor, fumarate. These results demonstrate that it is possible to enhance the ability of microorganisms to electrochemically interact with electrodes with the appropriate selective pressure and that improved current production is associated with clear differences in the properties of the outer surface of the cell that may provide insights into the mechanisms for microbe-electrode interactions.
"ey and Malvankar , 2015 ) . Genetically eliminating the capacity for pili production ( Reguera et al . , 2005 ; Tremblay et al . , 2012 ) or diminishing pili conductivity ( Vargas et al . , 2013 ; Liu et al . , 2014 ) severely reduces Fe ( III ) oxide reduction and current production , whereas increasing expression of pili yields higher currents ( Yi et al . , 2009 ; Leang et al . , 2013 ) . In a similar manner , co - culture aggregates sharing electrons via DIET could not be established with a strain of G . metallireducens that could not produce pili ( Shrestha et al . , 2013b ; Rotaru et al . , 2014a , b ) . Other outer - surface proteins , including c - type cytochromes , are also required for "
[Show abstract][Hide abstract] ABSTRACT: Electrodes are unnatural electron acceptors, and it is yet unknown how some Geobacter species evolved to use electrodes as terminal electron acceptors. Analysis of different Geobacter species revealed that they varied in their capacity for current production. Geobacter metallireducens and G. hydrogenophilus generated high current densities (ca. 0.2 mA/cm2), comparable to G. sulfurreducens. G. bremensis, G. chapellei, G. humireducens, and G. uraniireducens, produced much lower currents (ca. 0.05 mA/cm2) and G. bemidjiensis was previously found to not produce current. There was no correspondence between the effectiveness of current generation and Fe(III) oxide reduction rates. Some high-current-density strains (G. metallireducens and G. hydrogenophilus) reduced Fe(III)-oxides as fast as some low-current-density strains (G. bremensis, G. humireducens, and G. uraniireducens) whereas other low-current-density strains (G. bemidjiensis and G. chapellei) reduced Fe(III) oxide as slowly as G. sulfurreducens, a high-current-density strain. However, there was a correspondence between the ability to produce higher currents and the ability to grow syntrophically. G. hydrogenophilus was found to grow in co-culture with Methanosarcina barkeri, which is capable of direct interspecies electron transfer (DIET), but not with Methanospirillum hungatei capable only of H2 or formate transfer. Conductive granular activated carbon (GAC) stimulated metabolism of the G. hydrogenophilus – M. barkeri co-culture, consistent with electron exchange via DIET. These findings, coupled with the previous finding that G. metallireducens and G. sulfurreducens are also capable of DIET, suggest that evolution to optimize DIET has fortuitously conferred the capability for high-density current production to some Geobacter species.
Frontiers in Microbiology 07/2015; 6:744. DOI:10.3389/fmicb.2015.00744 · 3.99 Impact Factor
"Evidence suggest that Geobacter sulfurreducens can also reduce CO 2 into a multicarbon compound by MES (Soussan et al., 2013; Table 1). G. sulfurreducens is a well-characterized electrigenic bacterium generating power densities in oBESs as high as 3.9 W/m 2 (Yi et al., 2009). G. sulfurreducens pre-grown with acetate as an electron donor and carbon source was also shown to have the capacity to accept electrons from a cathode to reduce fumarate (Gregory et al., 2004; Dumas et al., 2008) or uranium(VI; Gregory and Lovley, 2005) after the depletion of acetate. "
[Show abstract][Hide abstract] ABSTRACT: Powering microbes with electrical energy to produce valuable chemicals such as biofuels has recently gained traction as a biosustainable strategy to reduce our dependence on oil. Microbial electrosynthesis (MES) is one of the bioelectrochemical approaches developed in the last decade that could have critical impact on the current methods of chemical synthesis. MES is a process in which electroautotrophic microbes use electrical current as electron source to reduce CO2 to multicarbon organics. Electricity necessary for MES can be harvested from renewable resources such as solar energy, wind turbine or wastewater treatment processes. The net outcome is that renewable energy is stored in the covalent bonds of organic compounds synthesized from greenhouse gas. This review will discuss the future of MES and the challenges that lie ahead for its development into a mature technology.
Frontiers in Microbiology 03/2015; 6. DOI:10.3389/fmicb.2015.00201 · 3.99 Impact Factor
"Electron transfer can occur either through membraneassociated components  , soluble electron shuttles generated by specific bacteria , or highly conductive nanowires . Microorganisms that have been used in MFCs include pure cultures of obligatory and facultative anaerobic bacteria    and mixed bacterial cultures    and municipal and industrial wastewater   . "
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