Single-carbon catabolism in acetogens: analysis of carbon flow in Acetobacterium woodii and Butyribacterium methylotrophicum by fermentation and 13C nuclear magnetic resonance measurement

Abstract

The catabolism of methanol, formate, or carbon monoxide to acetate or butyrate or both was examined in two acetogenic bacteria. Butyribacterium methylotrophicum simultaneously transformed methanol and formate mainly to butyrate with concomitant H2 and CO2 production and consumption. In contrast, methanol plus CO was primarily converted to acetate, and only slight amounts of CO2 were produced. In vivo 13C nuclear magnetic resonance analysis of [13C]methanol transformation by B. methylotrophicum indicated that methanol was predominantly incorporated into the methyl of acetate, 13C02 was produced and then consumed, and butyrate was formed from the condensation of two acetate precursors. The analysis of the position of acetate labeled by a given 13C single-carbon substrate when B. methylotrophicum or Acetobacterium woodii was grown in the presence of a second one-carbon substrate indicated two trends: when methanol was consumed, CO, CO2, or formate predominantly labeled the acetate carboxyl; when CO was consumed, CO2 and formate were principally funneled into the acetate methyl group, and CO remained a better carboxyl precursor. These data suggest a model of acetate synthesis via the combined operation of two readily reversible single-carbon pathways which are linked by CO2. Anaerobic acetate-producing bacteria are generally referred to as acetogens (20). Besides using saccharides, most of the known acetogens also ferment single-carbon compounds to acetate, and under certain conditions, some produce butyrate (14, 41) and caproate (14). Bacterial growth on single-parbon substrates as both carbon and energy sources has been termed unicarbonotrophy (40). Most of the information on acetogen singlecarbon transformations derives from analysis of the glucose catabolism of Clostridium thermoaceticum (20). In this anaerobe, approximately one of every three acetates originates from two pyruvate carboxyl moieties. One pyruvate carboxyl yields the methyl group of acetate via CO2 and its subsequent reduction through free formate (2, 33), tetrahydrofolate (THF) derivatives (3, 24), and finally corrinoid one-carbon carriers (19, 37). The acetate carboxyl arises from the second pyruvate carboxyl group directly, without the involvement of free CO2 (29). Recent results of Drake et al. (12) and Hu et al. (15) indicate that CO also serves as an acetate carboxyl precursor in C. thermoaceticum cell

Growth kinetics of Acetobacterium sp. on methanol-formate in continuous culture

“…The possible utilization of formate as co-substrate with methanol has been reported (Kerby et al 1983;Loubière et al © 2000 The Society for Applied Microbiology, Journal of Applied Microbiology 88, 191-201 1987), but no thorough analysis of the effect of formate on growth and organic acid production by Acetobacterium has been presented. If it is assumed that formate is oxidized to CO 2 in the carbonyl branch, implying a generation of about two-thirds of a mole of ATP by a chemiosmotic mechanism, and that the methyl group is bound directly to the methyltransferase (Fig.…”

“…Anaerobic acetate-producing bacteria are generally referred to as acetogens (Ljungdahl and Wood 1982). Besides using saccharides, most of the known acetogens also ferment singlecarbon compounds to acetate and under certain conditions, some produce butyrate and caproate (Kerby et al 1983). Bacterial growth on single-carbon substrates has been termed unicarbonotrophy or methylotrophy (Zeikus 1983).…”

Competition between reductive acetogenesis and methanogenesis in the pig large‐intestinal flora

“…We investigated the effect of a specific methane inhibitor, 2-bromoethane sulphonic acid (BES), an analogue of coenzyme M which is unique to methanogens (Sparling and Baniels 1987) on I3CO, incorporation into SCFAs. Nuclear magnetic resonance (NMR) spectroscopy was used as it has been recognized as a powerful tool for analysing the incorporation routes of single carbon substrates into acetate (Kerby et al 1983). The experiments were conducted in the absence of H, and with 20 and 80% H, in the gas phase as the rate of H, supply is believed to determine the extent of acetate synthesis (Prins and Lankhorst 1977).…”

Methanol‐driven enhanced biological phosphorus removal with a syntrophic consortium

“…The theoretical maximum P/C MET ratio should be around 0.75 assuming that (i) the initial methanol was all converted to acetic acid (for every 4 mol of methanol 3 mol of acetic were formed); and (ii) the theoretical P/C ACET ratio was 0.5. Three different plausible hypotheses can explain the fact that the experimental P/C ratio was lower than the theoretical one: (i) part of the methanol was used for growth purposes; (ii) part of the methanol was anaerobically degraded in a different pathway than desired (e.g., acidogenic butyrate formation, Heijthuijsen and Hansen, 1986; Kerby et al, 1983, formaldehyde or methane production Florencio et al, 1993a; Gonzalez‐Gil et al, 1999); or (iii) part of the acetate was used by other microorganisms than PAOs (e.g., GAOs). The first hypothesis would explain only a 10% decrease in the P/C ratio, as 10% is the approximate amount of methanol devoted to growth and not transformed to acetate (Florencio et al, 1995).…”