Geobacter biofilms

THEORETICAL AND PRACTICAL CONSIDERATIONS FOR CULTURING Geobacter BIOFILMS IN MICROBIAL FUEL CELLS AND OTHER BIOELECTROCHEMICAL SYSTEMS... 

Operational Parameters Affecting the Growth of Geobacter Biofilms in BBSs... 

Figure 2.2 Schematic of a two-chambered MFC or an MEC configuration, both having an anode electrode (AE), where Geobacter biofilms catalyze the oxidation of the electron donor (Djg to Dgjj). A proton-exchange membrane separates the two chambers to allow the diffusion of protons (H" ) from the anode to the cathode chamber. In the MFC, the anode electrode is wired directly to the cathode electrode (CE), and the amount of electrons (e") generated by the anode biofilms is dependent on the reduction potential of the electron acceptor (reaction A to Ajg) used as catholyte. In the MEC, the cathode limitation is bypassed using a potentiostat, which sets a constant potential of the anode electrode versus a reference electrode (RE) and allows the H" " and the e" to combine on the cathode electrode to generate Hj.

The theoretical current-potential dependency derived as follows Equation 6.9), which has been successfully applied to fit experimentally measured current-potential dependencies for Geobacter biofilms [6,7], results directly from the Nemst Equation. 

The sigmoid-shaped dependency of catalytic current on anode potential, observed for Geobacter biofilms under turnover condition [23], also results directly from the Nernst Equation. This indicates that electron transfer between a Geobacter biofilm and an electrode is fast and not the limiting factor in catalytic current generation that is comparable in magnitude to that observed for conducted current under nonturnover condition for the same biofilm [6,7],)... 

Biofilms, Electroactive, Fig. 4 (a) Cyclic voltammogram of a Geobacter biofilm grown at 0.2 V vs. Ag/AgCl on a graphite rod electrode in substrate depleted (non turn-over) conditions Ei to E/ indicate formal potentials of the four detected redox couples of the biofilm (b) CV of the same biofilm in the presence of... 

Bond DR, Strycharz-Glaven SM, Tender LM, Torres Cl (2012) On electron transport through Geobacter biofilms. ChemSusChem 5(6) 1099-1105... 

Bond, D.R., Strycharz-Glaven, S.M., Tender, L.M. Torres, C.I. On electron transport throu geobacter biofilms. ChemSusChem 5 (2012), pp. 1099-1105. 

Within the realm of these approaches, immunogold labeling can be of great value to address questions about electron transfer. For example, it was established that cytochromes can be associated with nanowires [17], and that in Geobacter biofilms OmcZ is a released cytochrome accumulating near the electrode surface [84]. From this it was hypothesized that it performed the role of a catalyst for transferring electrons from the nanowire to the electrode surfoce. 

Biofilm image on carbon nanotube (CNT)-based anode obtained by SEM (b-c) biofilm images obtained using confocal laser scaiming microscopy (CLSM). Geobacter forms a biofilm in a macroscale MFC (a) 10 days after the start-up, 12 pm thick, and (b) 18 days after the startup, 40 pm thick. CLSM is capable of measuring the thickness of density of biofilm (Richter et al. [15])... 

The Massachusetts scientists constructed a bacterial fuel cell using graphite electrodes. The Geobacter grow naturally on the surface of the electrode, forming a stable biofilm. The overall reaction is... 

Inoue, K., Leang, C., Franks, A.E., Woodard, T.L., Nevin, K.P., and Lovley, D.R. (2011) Specific localization of the c-type cytochrome OmcZ at the anode surface in current-producing biofilms of Geobacter sulfurreducens. Environ. Microbiol Rep., 3 (2), 211-217. 

Richter, H., Nevin, K.P., Jia, H.F., Lowy, D.A., Lovley, D.R., and Tender, L.M. (2009) Cydic voltammetry of biofilms of wild type and mutant Geobacter sulfurreducens on fuel cell anodes indicates possible roles of OmcB, OmcZ type IV pili, and protons in extracellular electron transfer. Energy Environ. Sci., 2 (5), 506—516. 

S.F., Johnson, J.P., Woodard, T.L., Orloff, A.L., Jia, H., Zhang, M., and Lovley, D.R. (2008) Power output and coulombic efficiencies from biofilms of Geobacter sulfurreducens comparable to mixed community microbial fuel cells. Environ. Microbiol., 10 (10), 2505-2514. 

Reguera G, Nevin KP, Nicoll JS, Covalla SF, Woodard TL, Lovley DR. Biofilm and nanowire production leads to increased current in Geobacter sulfurreducens fuel cells. Appl Environ Microbiol 2006 72 7345-7348. 

Jain A, Gazzola G, Panzera A, Zanoni M, MarshE. Visible spectroelectrochemical characterization of Geobacter sulfurreducens biofilms on optically transparent indium tin oxide electrode. Electrochim Acta 2011 56 10776-10785. 

Liu Y, Kim H, Franklin RR, Bond DR. Linking spectral and electrochemical analysis to monitor c-type cytochrome redox status in hving Geobacter sulfurreducens biofilms. Chemphyschem 2011 12 2235-2241. 

Nevin KP, Kim BC, Glaven RH, Johnson JP, Woodard TL, Methe BA, DiDonato RJ, Covalla SF, Franks AE, Liu A, Lovley DR. Anode biofilm transcriptomics reveals outer surface components essential for high density current production in Geobacter sulfurre-ducens fuel cells. PLoS One 2009 4 e5628. 

Most studies of Geobacter-dmtn BESs use G. sulfurreducens strain (ATCC 51573), which is routinely grown in an anaerobic medium named DB described by Speers and Reguera [19]. We named the medium DB after Daniel Bond, at the University of Minnesota, who first described an anaerobic medium for culturing G. sulfurreducens in MFCs [38], and which we modified to make the DB medium by supplementing it with 10 ml 1 of a lOOx vitamin mixture [41] to promote biofilm growth and electroactivity. The medium is prepared from three stock solutions (Table 2.1) routinely stored at 4 °C (the mineral and vitamin mixes are also stored in the dark). 

Rollefson JB, Stephen CS, Tien M, Bond DR. Identification of an extracellular polysaccharide network essential for cytochrome anchoring and biofilm formation in Geobacter sulfurreducens. 1 Bacteriol 2011 193 1023-1033. 

Marsili E, Sun 1, Bond DR. Voltammetry and growth physiology of Geobacter sulfurreducens biofilms as a function of growth stage and imposed electrode potential. Electroanalysis 2010 22 865-874. 

Snider RM, Strycharz-Glaven SM, Tsoi SD, Erickson JS, Tender LM. Long-range electron transport in Geobacter sulfurreducens biofilms is redox gradient-driven. Proc Natl Acad Sci U S A 2012 109 15467-15472. 

Nevin KP, Richter H, Covalla S, Johnson J, Woodard T, Orloff A, Jia H, Zhang M, Lovley D. Power output and columbic efficiencies from biofilms of Geobacter sul-furreducens comparable to mixed community microbial fuel cells. Environ Microbiol 2008 10(10) 2505-2514. 

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