Clostridium ultunense sp. nov., a Mesophilic Bacterium Oxidizing Acetate in Syntrophic Association with a Hydrogenotrophic Methanogenic Bacterium

Abstract

A syntrophic acetate-oxidizing bacterium, strain BST (T = type strain), was isolated from a previously described mesophilic triculture that was able to syntrophically oxidize acetate and form methane in stoichiometric amounts. Strain BST was isolated with substrates typically utilized by homoacetogenic bacteria. Strain BST was a spore-forming, gram-positive, rod-shaped organism which utilized formate, glucose, ethylene glycol, cysteine, betaine, and pyruvate. Acetate and sometimes formate were the main fermentation products. Small amounts of alanine were also produced from glucose, betaine, and cysteine. Strain BST grew optimally at 37°C and pH 7. The G+C content of the DNA of strain BST was 32 mol%. A 16s rRNA sequence analysis revealed that strain BST was a member of a new species of the genus Closfridium. We propose the name Clostridium ultunense for this organism; strain BS is the type strain of C. ultunense.Anaerobic oxidations of fatty acids to hydrogen and carbon dioxide by proton-reducing bacteria are, from a thermodynamic point of view, very unfavorable reactions (38). Under standard conditions, these hydrogen-producing reactions are all endergonic. However, standard conditions are not the conditions that occur in most natural anaerobic environments; at a very low partial pressure of hydrogen, like the partial pressure achieved in the presence of hydrogenotrophs, such as methanogenic or sulfate-reducing bacteria, the oxidation reaction becomes exergonic (9, 48). By consuming hydrogen, the hydrogenotrophs can create conditions under which the protonreducing bacteria can perform oxidations that otherwise could not yield energy; i.e., the latter organisms depend entirely on the former to fulfill their function.Several different species of bacteria are able to oxidize fatty acids (38). Syntrophomonas wolfei degrades straight-chain fatty acids up to octanoate, forming acetate and propionate together with H,, in cocultures with either a methanogen or a sulfate reducer (25). Propionate is degraded to acetate, carbon dioxide, and H, by Syntrophobacter wolinii in cocultures with members of the genus Desulfovibrio (5). Clostridium blyantii oxidizes fatty acids with 4 to 11 carbon atoms in associations with several different hydrogen-utilizing bacteria (43). Acetic acid is associated with the lowest levels of energy released from the fatty acids degraded in syntrophic cooperations. Thus, the partial pressure of hydrogen has to be very low for this reaction to proceed, and the energy available is influenced by the electron acceptor used. Under standard conditions, acetate oxidation coupled to methane formation releases less energy than acetate oxidation coupled to sulfate reduction (AGO' = -31.0 kJ/mol and AGO' = -47.7 kJ/mol, respectively). The changes in free energy are also slightly greater at higher temperatures. Syntrophic oxidation of acetate has been observed with thermophilic and mesophilic cultures, as well as at moderate tem- peratures with both methanogenic and sulfate-reducing bacteria as the hydrogen-c...

Thermotoga lettingae sp. nov., a novel thermophilic, methanol-degrading bacterium isolated from a thermophilic anaerobic reactor.

“…In this case, acetate was converted within 36 days. Although slow growth of strain TMO T on acetate was observed, these results are in agreement with those for previously described acetate-degrading bacteria that are either thermophilic or mesophilic and coupled to a methanogenic partner or an electron acceptor (Zinder & Koch, 1984 ;Schnu$ rer et al, 1996 ;Hattori et al, 2000).…”

Microbial Diversity in Three-Stage Methane Production Process Using Food Waste

“…또한, bootstrap값은 1,000회의 resampled data로부터 계산하였다 (Felsenstein, 1985). (Schnürer et al, 1996)로 3단계 메탄생성 공정에서 VFA의 분해에 관여함 을 알 수 있다.…”

Biogas process parameters—energetics and kinetics of secondary fermentations in methanogenic biomass degradation

“…This ratio may be shifted under specific conditions (enhanced temperature, high nitrogen loads) by homoacetogenesis (Ragsdale and Pierce 2008) or syntrophic acetate oxidation (Schnürer et al 1996). This link could also be used as a side channel to the opposite side in case of a limitation or promotion of only one group of the methanogenic partners involved.…”