Electron Transport in the Pathway of Acetate Conversion to Methane in the Marine Archaeon Methanosarcina acetivorans

An unconventional pathway for reduction of CO 2 to methane in CO-grown Methanosarcina acetivorans revealed by proteomics

“…2, steps 12 and 13) was demonstrated previously (17). Both enzymes were Ϸ4-fold less abundant in CO-grown versus acetate-grown cells (Table 1); however, 50-and 18-fold greater amounts of acetate kinase and phosphotransacetylase are reported for acetate-grown versus methanol-grown M. acetivorans (27), suggesting substantial amounts of both enzymes in acetate-grown cells. Thus, although lower amounts were detected in CO-grown versus acetate grown cells (Table 1), the levels of acetate kinase and phosphotransacetylase have the potential to supply adequate amounts for synthesis of acetate from acetyl-CoA during growth on CO.…”

“…Enzymes catalyzing steps 2, 3, 5, and 6 were at least 10-fold more abundant in CO-grown versus acetate-grown M. acetivorans, and the enzyme catalyzing step 4 was 2-fold greater (Table 1). These steps and enzymes are not involved in acetate fermentation to methane (27); thus, the results suggest these enzymes are differentially abundant in response to CO and support roles in steps 2-6. Further, M. acetivorans, like other Methanosarcina species, utilizes a reversal of steps 2-6 in the pathway of methanol dismutation to CO 2 and CH 4 (28,29); thus, the finding that each of the five enzymes was at approximately the same levels in CO-grown versus methanol-grown cells further supports roles in steps 2-6 (Fig.…”

“…The genome of M. acetivorans is annotated with a gene cluster (MA1495-MA1507) encoding a Fpo complex for which the products of 11 subunits were found in CO-grown M. acetivorans at approximately the same levels as in methanol-grown cells (Table 1). Furthermore, the amounts were considerably more abundant in CO-grown versus acetate-grown cells where the Fpo complex does not function (27). F 420 H 2 :CoB-S-S-CoM oxidoreductase activity in cell extracts of CO-grown M. acetivorans was approximately 2-and 10-fold greater than for methanol-and acetate-grown cells, respectively (Table 3).…”

“…In marine environments sulfate-reducing microbes outcompete methanogens for H 2 (49); thus, if H 2 was an intermediate in metabolism, it could be lost to sulfate reducers. Indeed, it was shown recently that the electron transport chain in acetate-grown M. acetivorans does not involve H 2 (27) in contrast to acetate-grown freshwater Methanosarcina species for which it is proposed that H 2 and the Ech hydrogenase plays an essential role in electron transport and energy conservation (39,48).…”

Catalytic Properties of Staphylococcus aureus and Bacillus Members of the Secondary Cation/Proton Antiporter-3 (Mrp) Family Are Revealed by an Optimized Assay in an Escherichia coli Host

“…In Sinorhizobium species, where dual systems have been named Pha1 and Pha2, mutational loss of Pha1 results in K ϩ sensitivity and a nitrogen fixation defect (48) while loss of Pha2 results in Na ϩ sensitivity (67). The recent observation of increased Mrp expression under specific metabolic conditions, e.g., during growth of the archaeon Methanosarcina acetivorans on acetate (35), suggests that additional settings in which Mrp has important roles will continue to be identified. In spite of their distribution and importance, Mrp antiporters are still very incompletely characterized, but they are clearly unique among monovalent cation/H ϩ antiporters.…”