Holmes, B. Postier, and R. Glaven, personal communications). The second pathway (Figure 1b) consists of two steps: acetate kinase (Gmet_1034 = GSU2707) converts acetate to acetyl-phosphate, which may be a global intracellular signal affecting various phosphorylation-dependent signalling systems, as in Escherichia coli [18]; and phosphotransacetylase (Gmet_1035 = GSU2706) converts acetyl-phosphate to acetyl-CoA [17]. Selleck MK 8931 G. metallireducens possesses orthologs of the enzymes of both pathways characterized in G. sulfurreducens [17], and also has an acetyl-CoA synthetase (Gmet_2340, 42% identical to the Bacillus subtilis enzyme [19]) for irreversible activation of acetate to acetyl-CoA at the expense

of two ATP (Figure 1c). Thus, Geobacteraceae such as G. metallireducens may be better suited to metabolize acetate at the low concentrations naturally found in most soils and sediments. Figure 1 Pathways of acetate activation in G. metallireducens. (a) The succinyl:acetate CoA-transferase reaction. (b) The acetate kinase and phosphotransacetylase reactions. (c) The acetyl-CoA synthetase reaction. Three enzymes distantly related to the succinyl:acetate CoA-transferases are encoded by Gmet_2054, Gmet_3294, and Gmet_3304, for which Captisol in vitro there are no counterparts in G. sulfurreducens. All three of these proteins closely match the characterized butyryl:4-hydroxybutyrate/vinylacetate CoA-transferases

of Clostridium species [20]. However, their substrate specificities may be different because the G. metallireducens proteins and the Clostridium proteins cluster phylogenetically with different CoA-transferases of Geobacter strain FRC-32 and Geobacter bemidjiensis (data not shown). The presence of these CoA-transferases indicates that G. metallireducens has evolved energy-efficient

activation steps for some unidentified organic acid substrates that G. sulfurreducens cannot utilize. Numerous other enzymes of acyl-CoA metabolism are predicted from the genome of G. metalllireducens but not that of G. sulfurreducens (Additional file 2: Table S2), including six gene Interleukin-3 receptor clusters, three of which have been linked to degradation of aromatic compounds that G. metallireducens can utilize [6, 21–23] but G. sulfurreducens cannot [24]. All seven acyl-CoA synthetases of G. sulfurreducens have orthologs in G. metallireducens, but the latter also possesses acetyl-CoA synthetase, benzoate CoA-ligase (experimentally validated [23]), and seven other acyl-CoA synthetases of unknown substrate find more specificity. The G. metallireducens genome also includes eleven acyl-CoA dehydrogenases, three of which are specific for benzylsuccinyl-CoA (69% identical to the Thauera aromatica enzyme [25]), glutaryl-CoA (experimentally validated [26]) and isovaleryl-CoA (69% identical to the Solanum tuberosum mitochondrial enzyme [27]), whereas none can be identified in G. sulfurreducens. G.