barkeri and in M. mazei are used to make the major formyl methanofuran dehydrogenase enzymes (Table 1). Interestingly, the M. barkeri genome

lacks the annotated fwd1 tungsten-type enzyme. Second, all sequenced Methanosarcina genomes contain multiple hdr genes encoding a membrane-type as well as a soluble-type heterodisulfide reductase (Table 1, Figure 2). Based on the transcript abundance studies in M. acetivorans, the membrane-type Hdr complex encoded by the hdrED1 genes was the most abundantly expressed gene cluster (Figure 2). This is consistent with the biochemical role for the membrane bound TGFbeta inhibitor enzyme in M. barkeri [7]. However, given the high transcript levels for the hdrA1 and hdrB1 genes in cells grown with either acetate or methanol, a physiological role is hereby predicted for a selleckchem soluble-type HdrABC heterodisulfide reductase in M. acetivorans

metabolism, and by inference, in M. mazei and M barkeri. The presence of a poly-ferredoxin-like gene immediately downstream of the hdrA1 gene (Figure 2B) provides one candidate for electron transfer from primary electron donors (i.e., from methanol via either formyl methanofuran dehydrogenase, or from acetate via carbon monoxide dehydrogenase) to this Hdr find more soluble-type enzyme (discussed below). Transcript abundance for both the hdrED1 and hdrA1B1 genes were within the same magnitude observed for the fpoN and fpoL genes (Figure 3C) that encode subunits of the F420 H2 dehydrogenase needed for central carbon flow to carbon dioxide. Since genes for both a membrane-type and a soluble-type Hdr enzyme are co-expressed,

this suggests that multiple pathways exist for electron transfer and/or energy conservation in M. acetivorans. By inference, the homologous hdrA pfd and hdrC1B1gene sets in M. DNA ligase barkeri and M. mazei are also highly expressed and operative. The energetic implication for having distinct Hdr-type enzymes is unknown. Possibilities include adaptation to different substrate levels and/or alternative modes of energy conservation [20]. Third, regarding the M. acetivorans sets of frh, vhtG1, and vhtG2 genes (Figure 3), plus the two electron transfer complexes encoded by rnfXCDGEABY and mrpABCDEFG genes (Figure 4), only the vhtG1, rnf and mrp gene sets were abundantly expressed. The vhtG1A1C1D1gene cluster encoding a methanophenazine-linked type hydrogenase was expressed at four- to six-fold higher levels during methanol growth conditions, and within the range seen for the fpoL and fpoN genes needed for methyl group oxidation for methanol and acetate metabolism. This is also in the range seen for methanol-dependent fmdA1, and fwdA1 expression (Figure 1). In contrast, no vht gene expression was detected in M. acetivorans when a vht-uidA promoter assay system was used [21]. Whether the high vhtG1 and vhtC1 mRNA levels detected here (Figure 3) versus the low values by the vht-uidA promoter assay is due to strain differences, cell growth, and/or in the analytical methods used is unknown.