Nitrite as an Energy-Conserving Electron Sink for the Acetogenic Bacterium Moorella thermoacetica

Abstract

Nitrite served as an energy-conserving electron acceptor for the acetogenic bacterium Moorella thermoacetica. Growth occurred in an undefined (0.1% yeast extract) medium containing 20 m M glyoxylate and 5 m M nitrite and was essentially equivalent to that observed in the absence of nitrite. In the presence of nitrite, acetate (the normal product of glyoxylate-derived acetogenesis) was not detected during growth. Instead, growth was coupled to nitrite dissimilation to ammonium, and acetogenesis was limited to the stationary phase. Furthermore, membranes from glyoxylate-grown cells under nitrite-dissimilating conditions were deficient in the b-type cytochrome that is typically found in the membranes of acetogenic cells. Unlike glyoxylate, other acetogenic substrates (fructose, oxalate, glycolate, vanillin, and hydrogen) were not growth supportive in the undefined medium containing nitrite, and glyoxylate-dependent growth did not occur in a nitrite-supplemented, basal (without yeast extract) medium. Glyoxylate-dependent growth by Moorella thermoautotrophica was not observed in the undefined medium containing nitrite.

Physiology of the thermophilic acetogen Moorella thermoacetica

“…Further evidence that oxalate, glyoxylate, and glycolate are metabolized via distinct mechanisms in M. thermoacetica has been obtained from observing the growth--supporting abilities of these substrates under nitratesupplemented basal culture conditions. In the presence of nitrate, oxalate and glyoxylate, unlike glycolate and other substrates (H2, CO, and methoxyl groups), are growth supportive for M. thermoacetica [107][108][109]. Oxalate--and glyoxylate--grown cells appear able to bypass the repression of the acetyl--CoA pathway by rerouting reductant or carbon flow or both during growth under nitrate--supplemented conditions (see Section 2.4).…”

“…Abbreviations: THF, tetrahydrofolate; CoA, coenzyme--A; Co--Protein, corrinoid enzyme. The dissimilation of nitrite to ammonium appears to have the same affect [109]. Modified from [34].…”

“…Ironically, if M. thermoacetica had been isolated in the presence of nitrate, its acetogenic nature might not have been discovered. Both nitrate and nitrite are used by M. thermoacetica as energy conserving terminal electron acceptors [106,109]. The dissimilation of nitrate can significantly increase the growth efficiency of M. thermoacetica.…”

“…Cellulose has recently been described as a substrate for an organism that is phylogenically closely related to M. thermoacetica [56]. b Nitrite can serve an electron acceptor during glyoxylate--dependent growth [109]. Pyruvate appears to also be reduced to lactate, since lactate can be produced when levels of available hexose--derived reductant is high (Fröstl and Drake, unpublished [31,58].…”

Regulation of Caffeate Respiration in the Acetogenic Bacterium Acetobacterium woodii

“…The best-studied example in the acetogens is M. thermoacetica, which can use CO 2 or nitrate as an electron acceptor (17). Nitrate is the preferred electron acceptor for M. thermoacetica, and nitrate reduction is coupled to energy conservation (43,44). The amount of energy conserved is larger during nitrate reduction than during acetogenesis with O-methyl groups.…”