One substrate, many fates: different ways of methanol utilization in the acetogen Acetobacterium woodii

Abstract

Summary Acetogenic bacteria such as Acetobacterium woodii use the Wood–Ljungdahl pathway (WLP) for fixation of CO2 and energy conservation. This pathway enables conversion of diverse substrates to the main product of acetogenesis, acetate. Methyl group containing substrates such as methanol or methylated compounds, derived from pectin, are abundant in the environment and a source for CO2. Methyl groups enter the WLP at the level of methyltetrahydrofolic acid (methyl‐THF). For methyl transfer from methanol to THF a substrate‐specific methyltransferase system is required. In this study, we used genetic methods to identify mtaBC2A (Awo_c22760‐Awo_c22740) as the methanol‐specific methyltransferase system of A. woodii. After methyl transfer, methyl‐THF serves as carbon and/or electron source and the respiratory Rnf complex is required for redox homeostasis if methanol + CO2 is the substrate. Resting cells fed with methanol + CO2, indeed converted methanol to acetate in a 4:3 stoichiometry. When methanol was fed in combination with other electron sources such as H2 + CO2 or CO, methanol was converted Rnf‐independently and the methyl group was condensed with CO to build acetate. When fed in combination with alternative electron sinks such as caffeate methanol was oxidized only and resulting electrons were used for non‐acetogenic growth. These different pathways for the conversion of methyl‐group containing substrates enable acetogens to adapt to various ecological niches and to syntrophic communities.

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

“…The substrates that feed carbon into the pathway after methylene‐THF are methyl group‐containing substrates. Indeed, we did show very recently, that methanol + CO 2 can be used as an electron sink; excess electrons are used to reduce CO 2 to CO which is then condensed with the methyl group and CoA to acetyl‐CoA (Kremp et al, 2018; Litty et al, 2022). Here, we used glycine betaine as methyl group donor.…”

“…It allows growth on C1 compounds such as H 2 + CO 2 , formate, methyl groups and carbon monoxide (Diekert & Thauer, 1978; Genthner & Bryant, 1982; Kremp et al, 2018; Kremp & Müller, 2021; Lechtenfeld et al, 2018; Litty et al, 2022; Moon et al, 2021; Stupperich & Konle, 1993; van der Meijden et al, 1984; Weghoff & Müller, 2016; Wood et al, 1986). The WLP allows to conserve energy, either by the pathway itself, for example the formyl‐THF synthetase in the oxidative reaction during methyl group oxidation (Kremp et al, 2018; Kremp & Müller, 2021; Lechtenfeld et al, 2018; Litty et al, 2022; Moon et al, 2023), or by a respiratory chain involved in redox balancing (Hess, Schuchmann, & Müller, 2013). However, the amount of ATP generated is small compared to the amount of ATP generated by glycolysis and the acetate kinase reaction.…”

“…The WLP enables acetogens to grow lithotrophically on H 2 + CO 2 according to: The WLP also enables acetogens to grow on other C1 substrates that are intermediates of the pathway such as formate (Moon et al, 2021), CO (Diekert & Thauer, 1978; Diender et al, 2015; Genthner & Bryant, 1982; Savage et al, 1987; Weghoff & Müller, 2016) or methyl groups (Bache & Pfennig, 1981; Kremp et al, 2018; Kremp & Müller, 2021; Lechtenfeld et al, 2018; Litty et al, 2022; Stupperich & Konle, 1993; van der Meijden et al, 1984).…”

Exploitation of a Type 1 Toxin–Antitoxin System as an Inducible Counter-Selective Marker for Genome Editing in the Acetogen Eubacterium limosum

“…These allow acetogens to incorporate methyl groups from various substrates into the Wood–Ljungdahl Pathway (WLP). A methanol methyltransferase was previously described in E. callanderi [ 24 ] and more recently in A. woodii [ 25 ]. Accordingly, we targeted mtaA (WP_038352459.1) and mtaC (WP_038352387.1) which respectively encode methylcobalamin:tetrahydrofolate methyltransferase (MtaA) and the associated corrinoid-binding protein (MtaC) which transfers methyl groups to tetrahydrofolate.…”

Thermophilic Moorella thermoacetica as a platform microorganism for C1 gas utilization: physiology, engineering, and applications

“…1 ); thus, M. thermoacetica appears to be a potential platform microorganism for formate bioconversion, although further improvements in its tolerance and consumption to formate are needed. Regarding methanol, its assimilation in microorganisms typically employs two approaches: integration of methanol into the WL pathway via methanol methyltransferase, and oxidization of methanol to formaldehyde and formate, which are further assimilated through downstream pathways (Bae et al 2022 ; Litty et al 2022 ). The former approach has been identified in a representative acetogenic bacterium, Acetobacterium woodii (Litty et al 2022 ; Wang et al 2023 ).…”