The electron transport of marine acetate-utilizing methanogen Methanosarcina acetivorans was investigated, leading to the first identification and partial characterization of two novel ferredoxin: CoM-S-S-CoB electron transport chains. The study of an Rnf-dependent membrane-bound pathway of aceticlastic M. acetivorans that doesn’t reduce CO₂ with H2 characterized members both unique to Rnf-dependent pathway and also in common with Ech-dependent ferredoxin: CoM-S-S-CoB electron transport chain in CO₂ utilizing aceticlastic methanogens. These include the Rnf complex, cytochrome c, ferredoxin, Cdh, methanophenazine, heterodisulfide reductase and CoM-S-S-CoB. The purification and phylogenetic analysis of ferredoxin suggested an aceticlastic-specific ferredoxin clade among methanogens. This Rnf-dependent electron transport pathway, shared with non-CO₂ utilizing Methanosarcina thermophila is analogous to Ech-dependent electron transport pathway in its location and terminal electron partners but differs from the later in that it lacks the use of hydrogenases and H₂. A novel soluble ferredoxin: CoM-S-S-CoB pathway was identified in M. acetivorans by comparing soluble and membrane-bound ferredoxin: CoM-S-S-CoB oxidoreductase activities and was hypothesized to involve a HdrA: MvhD fusion protein, named Etp. Etp was heterologously overexpressed in Escherichia coli, purified, reconstituted and partially characterized for the first time, showing heavy iron-sulfur cluster content. The reduction of Etp is linked to the oxidation of ferredoxin mediated by unknown soluble factors. Finally, a model of energy conservation for M. acetivorans was constructed suggesting this soluble electron transport chain serves to bypass certain energy coupling sites and maximize energy conservation efficiency under substrate-limited scenarios.