Geobacter sulfurreducens

Cell suspensions of Geobacter sulfurreducens can conple the oxidation of hydrogen to the reduction of Tc(VII) to insolnble Tc(IV). An indirect mechanism involving Fe(II) was also observed, and was snbstantially increased in the presence of the redox mediator AQDS (Lloyd et al. 2000). 

Kaufmann F, DR Lovley (2001) Isolation and characterization of a soluble NADPH-dependent Fe(lll) reductase from Geobacter sulfurreducens. J Bacteriol 183 4468-4476. 

Seeliger S, R Cord-Ruwisch B Schink (1998) A periplasmic and extracellular c-type cytochrome of Geobacter sulfurreducens acts as a ferric iron reductase and as an electron carried to other acceptors or to partner bacteria. J Bacteriol 180 3686-3691. 

The reductase in Geobacter sulfurreducens is located in the outer membrane and a soluble Fe(III) reductase has been characterized from cells grown anaerobically with acetate as electron donor and Fe(III) citrate or fumarate as electron acceptor (Kaufmann and Lovley 2001). The enzyme contained Fe, acid-labile S, and FAD. An extracellular c-type cytochrome is distributed in the membranes, the periplasm, and the medium, and functions as a reductase for electron transfer to insoluble iron hydroxides, sulfur, or manganese dioxide (Seeliger et al. 1998). 

Lin WC, MV Coppi, DR Lovley (2004) Geobacter sulfurreducens can grow with oxygen as terminal electron acceptor. Appl Environ Microbiol 70 2525-2528. 

Caccavo F, Lonergan DJ, Lovley DR, Davis M, Stolz JF, Mclnemey MJ (1994) Geobacter sulfurreducens sp. nov., a hydrogen- and acetate-oxidizing dissimilatory metal-reducing microorganism. App Environ... 

Gaspard S, Vazques F, Holliger C (1998) Localization and solubilization of the Fe(II) reductase of Geobacter sulfurreducens. App Environ Microbio 64 3188-3194... 

Magnuson TS, Hodges-Myerson AL, Lovley DR (2000) Characterization of a membrane-bound NADH-dependent Fe + reductase from the dissimilatory Fe -reducing bacterium Geobacter sulfurreducens. FEMS Microbio Lett 185 205-211... 

Treponema pallidum Treponema denticola A Geobacter sulfurreducens Escherichia coli Salmonella typhi Yersinia enterocolitica Yersinia pestis Erwinia chrysanthemi A... 

Since both Geobacter metallireducens and Geobacter sulfurreducens have triheme cyt C7 proteins (Champine et al. 2000, Afkar and Fukumori 1999 Seeliger et al. 1998), it is appropriate to consider that these electron carriers function in metal reduction in a manner similar to that reported for the cyt C7 of D. acetooxidans. The role of other cytochromes in Geobacter has not been explored with respect to metal reduction. 

Galushko AS, Schink B. 2000. Oxidation of acetate through reaction of the citric acid cycle by Geobacter sulfurreducens in pure culture and in syntrophic coculture. Arch Microbiol 174 314-21. 

Another superfamily is formed by bacterial di-heme CCP (with over 110 entries in PeroxiBase) that are periplasmic enzymes providing protection from oxidative stress. These homodimeric enzymes have a conserved tertiary structure containing two type-c hemes covalently attached to two predominantly a-helical domains via a characteristic binding motif. One heme acts as a low redox-potential center where H2O2 is reduced, and the other as a high redox-potential center that feeds electrons to the peroxidatic site from soluble electron-shuttle proteins such as cytochrome c [24]. In the crystal structure of the Geobacter sulfurreducens enzyme shown in Fig. 3.1g, the first heme appears as a bis-histidinyl-coordinated form (and... 

As previously mentioned (p. 7), bacteria like S. oneidensis and G. metallireducens have the capacity to reduce insoluble Mn02 to soluble Mn + enzymatically by anaerobic respiration with a suitable electron donor in a direct process in which the respective organisms attach to the surface of the oxide. In the case of S. oneidensis, the electron donor may be lactate, pyruvate, formate or H2, but not acetate. The lactate and pyruvate are oxidized to acetate as end-product. Geobacter metallireducens can use butyrate, propionate, lactate and acetate as electron donors, but not H2 or formate, and oxidizes the organic electron donors completely to CO2 and H2O. Geobacter sulfurreducens can use H2 as electron donor in Mn02 reduction (see Lovley, 2000). 

Cord-Ruwisch R., Lovley D. R., and Schink B. (1998) Growth of Geobacter sulfurreducens with acetate in syntrophic cooperation with hydrogen-oxidizing anaerobic partners. Appl. Environ. Microbiol. 64, 2232-2236. 

Kaden J., Galushko A. S., and Schink B. (2002) Cysteine-mediated electron transfer in syntrophic acetate oxidation by co-cultures of Geobacter sulfurreducens and Wolinella succinogenes. Arch. Microbiol. 178, 53—58. 

FIGURE 7.4 F roposed models depicting electron transfer pathways for Shewanella oneidensis MR-1 (a) and Geobacter sulfurreducens (b) during dissimilatory reduction of solid metal (hydr)oxides. (From Shi, Squier, Zachara i4 Fredrickson, 2007.)... 

A membrane-bound NADH-dependent ferric iron reductase has been obtained from Geobacter sulfurreducens (Magnuson et al., 2000). The enzyme contains a hemoprotein and FAD. the reduced hemoprotein in the enzyme is reoxidized on addition of ferric ion and NADH is a specific electron donor for the enzyme. The bacterium has a citric acid cycle (TCA cycle) (Galushko and Schink, 2000). Besides G. metallireducens and G. sulfurreducens, several bacteria of Geobacter genus have been isolated, namely G. bremensis, G. pelophilus (Straub and Buchholz-Cleven, 2001), G. hydrogenophilus, G. chapelli, and G. grbiciae (Coates et al., 2001). 

Furukawa Y, Inubushi K (2002) Feasible suppression technique of methane emission from paddy soil by iron amendment. Nutr Cycl Agroecosyst 64 193-201 Fuseler K, Krekeler D, Sydow U, Cypionka H (1996) A common pathway of sulfide oxidation by sulfate-reducing bacteria. FEMS Microbiol Lett 144 129-134 Galushko AS, Schink B (2000) Oxidation of acetate through reactions of the citric acid cycle by Geobacter sulfurreducens in pure culture and in syntrophic coculture. Arch Microbiol 174 314-321... 

Geobacter sulfurreducens 2.50 2000 Iron reduction/biomining, biocatalysts... 

These experiments pointed out that respiratory reduction of As(V) sorbed to solid phases can indeed occur in nature, but its extent and the degree of mobilization of the As(III) product is constrained by the type of minerals present in a given system. What remains unclear is whether micro-organisms can actually reduce As(V) while it is attached to the mineral surface, or if they attack a mono-layer of aqueous As(V) that is in equilibrium with the As(V) adsorbed onto the surface layer. If, as is the case for dissimilatory metal-reducing bacteria such as Geobacter sulfurreducens and Shewanella oneidensis (44,45), components of the electron transport chain are localized to the outer-membrane of some arsenate-respiring bacteria, direct reductive dissolution of insoluble arsenate minerals may be possible by attached bacteria. Too little is known at present about the topology... 

S Gaspard, F Vazquez, and C Holliger. Locahzation and solubilization of the iron (III) reductase of Geobacter sulfurreducens. J Bacteriol 64 3188-3194. 

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