Growth of the acetogenic bacterium Acetobacterium woodii by dismutation of acetaldehyde to acetate and ethanol

Abstract

Acetogenic bacteria are a group of strictly anaerobic bacteria that may have been first life forms on Earth since they employ an ancient pathway for CO 2 fixation into acetyl-CoA that is coupled to the synthesis of ATP, the Wood-Ljungdahl pathway. Electrons for CO 2 reduction are derived from oxidation of H 2 or CO and thus, these bacteria can grow lithotrophically on gases present on early Earth. Among the organic molecules present on early Earth is acetaldehyde, a highly volatile C2 compound. Here, we demonstrate that the acetogenic model bacterium Acetobacterium woodii grows on acetaldehyde. Acetaldehyde is dismutated to ethanol and acetyl-CoA, most likely by the bifunctional alcohol dehydrogenase AdhE. Acetyl-CoA is converted to acetate by two subsequent enzymes, phosphotransacetylase and acetate kinase, accompanied by the synthesis of ATP by substrate-level phosphorylation. Apparently, growth on acetaldehyde does not employ the Wood-Ljungdahl pathway. Our finding opens the possibility of a simple and ancient metabolic pathway with only three enzymes that allows for biomass (acetyl-CoA) and ATP formation on early Earth.

Exploring Bacterial Microcompartments in the Acetogenic Bacterium Acetobacterium woodii

“…Interestingly, induction by acetaldehyde was mere 2-fold higher than in the control where no inducer was added (formate only). Since the first step in metabolism of acetaldehyde by A. woodii involves the key enzyme AdhE to produce ethanol and acetyl-CoA ( Trifunovic et al, 2020 ), it might be the case that ethanol is the actual inducer of pdu operon during growth on acetaldehyde. Since the reporter gene assay was carried out in a 24 h time frame and no growth was observed on addition of acetaldehyde, possibly low ethanol formation resulted in low induction of the reporter gene.…”

A new metabolic trait in an acetogen: Mixed acid fermentation of fructose in a methylene‐tetrahydrofolate reductase mutant of Acetobacterium woodii

“…Acetogens are metabolically very versatile and can also grow heterotrophically on sugars, carboxylic acids and aldehydes (Bache & Pfennig, 1981; Drake et al, 2008; Gößner et al, 1994; Moon et al, 2019; Seifritz et al, 1999; Trifunovic et al, 2020; Weghoff et al, 2015). Actually, the WLP was discovered during glucose fermentation in Moorella thermoacetica (formerly Clostridium thermoaceticum ; Fontaine et al, 1942).…”

Adh4, an alcohol dehydrogenase controls alcohol formation within bacterial microcompartments in the acetogenic bacterium Acetobacterium woodii

“…Our earlier studies have shown that BMCs are not only produced during growth on 1,2‐PD but also during heterotrophic growth of A. woodii on ethanol (Bertsch et al ., 2016), acetaldehyde (Trifunovic et al ., 2020), 2,3‐butanediol (2,3‐BD) (Hess et al ., 2015), ethylene glycol (Trifunović et al ., 2016) or fructose (Schuchmann et al ., 2015). During growth on many of these substrates, alcohol dehydrogenases apparently play an important role.…”

“…During growth on many of these substrates, alcohol dehydrogenases apparently play an important role. While the A. woodii genome encodes 11 putative Adhs, only the bifunctional AdhE has been purified and characterized to be the key enzyme involved in ethanol and acetaldehyde metabolism of A. woodii (Bertsch et al ., 2016; Trifunovic et al ., 2020). However, during growth on either 1,2‐PD or 2,3‐BD, AdhE was not produced by A. woodii .…”