Methanol and methyl group conversion in acetogenic bacteria: biochemistry, physiology and application

Abstract

The production of bulk chemicals mostly depends on exhausting petroleum sources and leads to emission of greenhouse gases. Within the last decades the urgent need for alternative sources has increased and the development of bio-based processes received new attention. To avoid the competition between the use of sugars as food or fuel, other feedstocks with high availability and low cost are needed, which brought acetogenic bacteria into focus. This group of anaerobic organisms uses mixtures of CO2, CO and H2 for the production of mostly acetate and ethanol. Also methanol, a cheap and abundant bulk chemical produced from methane, is a suitable substrate for acetogenic bacteria. The microorganisms with the ability to convert methanol (or methyl groups from other sources) are summarized in the group of methylotrophs that includes aerobic as well as anaerobic organisms like acetogens. In methylotrophic acetogens the methyl group is transferred to the Wood-Ljungdahl pathway, a pathway to reduce CO2 to acetate via a series of C1-intermediates bound to tetrahydrofolic acid. Here we describe the biochemistry and bioenergetics of methanol conversion in the biotechnologically interesting group of anaerobic, acetogenic bacteria. Further, the bioenergetics of biochemical production from methanol is discussed.

Butyrate production in the acetogen Eubacterium limosum is dependent on the carbon and energy source

“…Here we describe for the first time that the acetogen E. limosum KIST612 produces butyrate from methanol. Growth on methanol requires the action of a methyltransferase system that transfers the methyl group from methanol to tetrahydrofolate and E. limosum KIST612 has a gene cluster similar to a previously suggested methanol-specific methyltransferase system of A. woodii (Kremp and Müller, 2020). Buytrate production from acetyl-CoA follows the pathways described for example for Clostridium acetobutylicum (Dürre et al, 2002) involving thiolase, hydroxybutyryl-CoA dehydrogenase, crotonase and butyryl-CoA dehydrogenase with the exception, that the latter is electron-bifurcating and reduces ferredoxin alongside with crotonyl-CoA (Jeong et al, 2015).…”

Production of the biocommodities butanol and acetone from methanol with fluorescent FAST-tagged proteins using metabolically engineered strains of Eubacterium limosum

“…The C1 carbon sources clearly influenced the product spectrum of E. limosum , since high amounts of methanol (200 mM) resulted in improved butyrate production titers. Methanol is oxidized to CO 2 via the WLP which provides three mol NAD(P)H per methyl group oxidized [ 45 , 47 ]. The NAD(P)H-NAD(P) + balance is regulated during butyrate production since the reactions catalyzed by 3-hydroxybutyryl-CoA dehydrogenase and crotonase are NADH dependent and, therefore, regenerate NAD(P) + .…”

“…Thus, the acetate:butyrate ratio shifts in favor of butyrate when cells grow on methanol [ 46 ]. Moreover, the utilization of methanol yields 1.83 ATP/butyrate, while H 2 + CO 2 utilization only yields 1 ATP/butyrate [ 47 ]. As shown for C. autoethanogenum and A. woodii mutants, improved ATP supply benefits fast growth and abolishes acetate production [ 48 , 49 ].…”

Production of the Biocommodities Butanol and Acetone from Methanol with Fluorescent FAST-tagged Proteins using Metabolically Engineered Strains of Eubacterium Limosum

“…Thus, the acetate:butyrate ratio shifts in favor of butyrate when cells grow on methanol [47]. Moreover, the utilization of methanol yields 1.83 ATP/butyrate, while H 2 + CO 2 utilization only yields 1 ATP/butyrate [48]. As shown for C. autoethanogenum and A. woodii mutants, improved ATP supply bene ts fast growth and abolishes acetate production [49,50].…”

“…Natural butanol production from C1 gases is reported for the to E. limosum closely related methanol-utilizing acetogen Butyribacterium methylotrophicum [54]. In B. methylotrophicum, the production of one mol butanol from methanol requires six reducing equivalents and yields 1.5 ATP/butanol [48].…”