(Gmet_3169, 48% identical) that has no homolog in G. sulfurreducens. In the catabolic direction, in addition to pyruvate kinase (Gmet_0122 = GSU3331) that converts phosphoenolpyruvate to pyruvate plus ATP, G. metallireducens has a homolog of E. coli phosphoenolpyruvate carboxylase (Gmet_0304, 30% identical, also found in Geobacter FRC-32) that may convert phosphoenolpyruvate to oxaloacetate irreversibly (Figure 3b) and contribute to the observed futile cycling of pyruvate/oxaloacetate/phosphoenolpyruvate  if not tightly regulated. Thus, control of the fate of pyruvate appears to be more complex in G. metallireducens than in G. sulfurreducens. Figure 3 Potential futile cycling of pyruvate/oxaloacetate selleck inhibitor and phosphoenolpyruvate in G. metallireducens. (a) Conversion of pyruvate to phosphoenolpyruvate. (b) Conversion of phosphoenolpyruvate to pyruvate or oxaloacetate. Evidence of recent fumarate respiration in G. metallireducens The succinate dehydrogenase complex of G. sulfurreducens also functions as a respiratory fumarate reductase, possibly in association with a co-transcribed b-type cytochrome . G. metallireducens has homologous genes (Gmet_2397-Gmet_2395 = GSU1176-GSU1178), but is unable to grow
with fumarate as the terminal GDC 941 electron acceptor unless transformed with a plasmid that expresses the dicarboxylic acid exchange transporter gene dcuB of G. sulfurreducens , which has homologues in Geobacter FRC-32, G. bemidjiensis, G. lovleyi, and G. uraniireducens. Surprisingly, G. metallireducens has acquired another putative succinate dehydrogenase or fumarate reductase complex (Gmet_0308-Gmet_0310), not found in other Geobacteraceae, by lateral gene transfer from a PLX3397 manufacturer relative of the Chlorobiaceae (phylogenetic trees not shown), and evolved it into a gene cluster that includes enzymes of central metabolism acquired from other sources (Figure 4). Thus, G. metallireducens may have actually enhanced its ability Molecular motor to respire fumarate before recently losing the requisite transporter.
Figure 4 Acquisition of a second fumarate reductase/succinate dehydrogenase by G. metallireducens. (a) The ancestral gene cluster. (b) The gene cluster acquired from a relative of the Chlorobiaceae, located near other acquired genes relevant to central metabolism: an uncharacterized enzyme related to succinyl-CoA synthetase and citrate synthase (Gmet_0305-Gmet_0306) and phosphoenolpyruvate carboxylase (Gmet_0304). Conserved nucleotide sequences (black stripes) were also identified in the two regions. Nitrate respiration and loss of the modE regulon from G. metallireducens G. metallireducens is able to respire nitrate , whereas G. sulfurreducens cannot . The nitrate reductase activity of G.