Chapter 10: Sulfur Respiration

Certain anaerobic prokaryotes grow by oxidative phosphorylation with elemental sulfur as the terminal electron acceptor instead of O2 (sulfur respiration or anaerobic respiration with sulfur). The mechanism of sulfur respiration has been investigated in great detail only inWolinella (W.) succinogenes. This e-proteobacterium uses, as terminal electron acceptor, polysulfide which is formed abiotically from elemental sulfur and sulfide. Polysulfide reduction is facilitated by a periplasmic sulfur-binding protein whose structure was determined. Polysulfide respiration with H2 or formate as electron donor is catalyzed by the membrane ofW.succinogenes and is coupled to apparent proton translocation across the membrane. The eletrochemical proton potential (Δp) thus generated and the corresponding H+/e– ratio were determined to be 170 mV (negative inside) and 0.5, respectively. The electron transport chain catalyzing polysulfide respiration by H2 or formate consists of polysulfide reductase, methyl-menaquinone and hydrogenase or formate dehydrogenase. Each enzyme consists of two different hydrophilic and a hydrophobic subunit which anchors the enzyme in the membrane. The membrane anchors of hydrogenase and formate dehydrogenase are similar di-heme cytochromesb which carry the site of quinone reduction. Methyl-menaquinone is thought to be bound to the membrane anchor of polylsulfide reductase and to accept electrons from the cytochromesb of the dehydrogenases. Proteoliposomes containing polysulfide reductase, methy-menaquinone, and formate dehydrogenase isolated fromw.succinogenes catalyze polysulfide reduction by formate which is coupled to Δp generation. The coupling mechanism is discussed.