Fig. 1
From: Assessing methanotrophy and carbon fixation for biofuel production by Methanosarcina acetivorans
Proposed methanogenesis reversal pathway supported by the iMAC868 model of M. acetivorans for co-metabolization of methane and bicarbonate in the presence of Fe3+ as external electron acceptor. Soluble and membrane-bound electron bifurcation routes are shown as blue and orange, respectively, and enzymes within ovals. In both routes, electrons originate from coenzyme B and coenzyme M. For enzymes with multiple subunits, only the subunits of soluble Hdr and Rnf involved in electron bifurcation are shown in detail. Numbers in italics next to enzyme ovals denote reaction fluxes (in mmol/gDCW-h) calculated under maximization of acetate production at bicarbonate to methane ratio of 0.44. This ratio corresponds to the maximum thermodynamically feasible value ensuring biomass production at 30Â % of its theoretical maximum for Fe3+ as the electron acceptor. The flux towards growth was calculated by assuming that 1Â g of biomass contains 36Â mmol of carbon. Intracellular proton and water stoichiometries are omitted for the sake of simplicity. Soluble methyltransferase (CmtA) is not present in the network since the minimum possible flux through this reaction is zero. Mcr * putative ANME-like Mcr homolog to methyl-coenzyme M reductase, HdrBC:HdrA:MvhD soluble ferredoxin-dependent heterodisulfide reductase, Mtr methyl-THSPT:coenzyme M methyltransferase, Mer methenyl-THSPT reductase, Mtd methenyl-THSPT dehydrogenase, Mch methenyl-THSPT cyclohydrolase, Ftr formylmethanofuran:THSPT formyltransferase, Fmd formylmethylfuran dehydrogenase, Cdh CO dehydrogenase, Pta phosphotransacetylase, Ack acetate kinase, Por pyruvate synthase, Atps ATP synthase, Mrp sodium/proton antiporter, Rnf methanophenazine reductase, Cyt cytochrome c subunit of Rnf complex, Fpo F420 dehydrogenase, Cam carbonic anhydrase, F4nr F420-dependent NADP reductase, THSPT tetrahydrosarcinapterin, MF methanofuran, MP methanophenazine, MPH 2 reduced methanophenazine, Fd o oxidized ferredoxin, Fd r reduced ferredoxin, F 420 coenzyme F420, F 420 H 2 reduced coenzyme F420