“…Owing to its physiological importance, the twoelectron reduction step of nitrate to nitrite and the corresponding enzymes have been extensively studied. However, the capacity to use nitrate has been discovered only in a few sulfate-reducing bacteria including Desulfovibrio (Senez & Pichinoty, 1958;Liu & Peck, 1981;McCready et al, 1983;Seitz & Cypionka, 1986;Keith & Herbert, 1983;Mitchell et al, 1986), Desulfobulbus (Widdel & Pfenning, 1982), Desulfomonas (Widdel & Pfenning, 1984) and Desulfobacterium (Szewzyk & Pfenning, 1987). Nitrate is reduced to ammonia in a respiratory process coupled to electrontransport phosphorylation (Seitz & Cypionka, 1986).…”