Transient Production of Formate During Chemolithotrophic Growth of Anaerobic Microorganisms on Hydrogen

Abstract

The homoacetogenic bacteria Acetobacterium woodii, A. carbinolicum, Sporomusa ovata, and Eubacterium limosum, the methanogenic archaeon Methanobacterium formicicum, and the sulfatereducing bacterium Desulfotomaculum orientis all produced formate as an intermediate when they were growing chemolithoautotrophically with H 2 and CO 2 as sources of energy, electrons, and carbon. The sulfate-reducing bacterium Desulfovibrio vulgaris grew chemolithoheterotrophically with H 2 and CO 2 using acetate as carbon source, but also produced formate when growth was limited by sulfate. All these bacteria were also able to grow on formate as energy source. Formate accumulated transiently while H 2 was consumed. The maximum formate concentrations measured in cultures of A. woodii and A. carbinolicum were proportional to the initial H 2 partial pressure, giving a ratio of about 0.5 mM formate per 10 kPa H 2 . The methanogen Methanobacterium bryantii, on the other hand, was unable to grow on formate and did not produce formate during chemolithoautotrophic growth on H 2 . The results indicate that the ability to utilize formate, that is, to possess a formate dehydrogenase, was the precondition for the production of formate during chemolithotrophic growth on H 2 .Formate is a typical product of mixed acid fermentation in enterobacteria and is formed by the pyruvate formate lyase [19]. Escherichia coli and related enterobacteria possess a formate-hydrogen lyase enzyme system that catalyzes the reversible conversion of formate to H 2 plus CO 2 [4,29]. Formate is also known to be a product when homoacetogenic bacteria are grown on hexoses, for example, Clostridium aceticum [16], Clostridium formicoaceticum, [1] and Peptostreptococcus productus [27]. Formate instead of H 2 is often produced when syntrophic bacteria grow on organic acids and alcohols, and then replaces H 2 in the so-called interspecies-formate-transfer to methanogenic archaea [5,13,34]. Many methanogenic archaea are able to utilize formate. They apparently route the formate into the metabolism via a formate-hydrogen lyase system consisting of formate dehydrogenase and hydrogenase [2,38]. Indeed, these methanogens were shown to produce formate from H 2 /CO 2 and, vice versa, H 2 from formate [3,38]. In digestive tracts in which significant activities of homoacetogenic formation of acetate from H 2 and CO 2 were detected, an H 2 -dependent formation of formate was also found [7,11,26,28]. Elevated H 2 concentrations in anoxic sediments and paddy soil give rise to elevated formate concentrations [9,10,25]. There is also a rapid isotopic exchange between formate and CO 2 [10]. Hence, one may hypothesize that anaerobic chemolithotrophic bacteria that are able to utilize alternatively H 2 /CO 2 or formate may be responsible for the formate production from H 2 /CO 2 observed in anoxic environments. Therefore, we systematically tested different anaerobic bacteria, that is, homoacetogens, sulfate reducers, and methanogens, that were able to grow on formate and on H 2 /CO 2 to determ...

Microbial Resource Management for Ex Situ Biomethanation of Hydrogen at Alkaline pH

“…Formate is an alternative electron donor for hydrogenotrophic methanogens [64] and a former study showed formate synthesis from H 2 /CO 2 by bacteria [65]. Furthermore, pure cultures of hydrogenotrophic methanogens (Methanobacterium formicicum) or acetogenic bacteria transiently produced formate during H 2 /CO 2 metabolism [66,67]. Hence, it can be inferred that homoacetogens, SAOB and hydrogenotrophic methanogens could have contributed to concomitant formate formation, along with methanogenesis.…”

Carbon monoxide conversion with Clostridium aceticum

“…Reduction of formate, an intermediate of the CO 2 reduction in the methyl branch of the reductive acetyl‐CoA pathway, takes four more reduction equivalents and one mol ATP. Thus formate accumulation indicates a disturbance of the reductive acetyl‐CoA pathway as it was observed for other acetogens, for example, Acetobacterium woodii , Sporomusa ovata , or Acetobacterium wieringae in acetogenic bacteria (Diekert & Wohlfarth, ; Groher & Weuster‐Botz, ; Kantzow & Weuster‐Botz, ; Mayer & Weuster‐Botz, ; Peters, Janssen, & Conrad, ). Strong initial formate accumulation occurred basically at p CO,in = 200 mbar but not at p CO,in = 500 mbar.…”

Growth of Dehalococcoides mccartyi species in an autotrophic consortium producing limited acetate

“…Strain F1 can generate formate and a small amount of acetate from consumption of H 2 and CO 2 . Generation of formate from H 2 /CO 2 by Desulfovibrio strains has been reported previously (Peters et al 1999), but only chemolithoheterotrophically (i.e., with acetate as fixed carbon source). It was suggested that possessing a formate dehydrogenase is the prerequisite for producing formate during chemolithotrophic growth on H 2 (Peters et al 1999).…”

“…strain G11 was claimed to be an autotroph, but no supporting experimental data were presented (McInerney et al 1981;Dolfing et al 2008). Mixotrophic growth with H 2 /CO 2 and acetate is more common with Desulfovibrio bacteria, e.g., D. desulfuricans (Londry and Marais 2003;Mechalas and Rittenberg 1960) and D. vulgaris (Peters et al 1999). Notably, formate was formed as an intermediate when D. vulgaris was grown chemolithoheterotrophically with H 2 /CO 2 and acetate under sulfate-limiting conditions (Peters et al 1999).…”

“…Mixotrophic growth with H 2 /CO 2 and acetate is more common with Desulfovibrio bacteria, e.g., D. desulfuricans (Londry and Marais 2003;Mechalas and Rittenberg 1960) and D. vulgaris (Peters et al 1999). Notably, formate was formed as an intermediate when D. vulgaris was grown chemolithoheterotrophically with H 2 /CO 2 and acetate under sulfate-limiting conditions (Peters et al 1999). To date, autotrophic sulfate reducers fall into two categories by the mechanisms they utilize to synthesize acetyl-CoA from CO 2 -the reductive citric acid cycle and the reductive CO-dehydrogenase pathway (acetyl-CoA pathway) (Rabus et al 2006).…”