Methanol and Carbon Monoxide Metabolism of the Thermophile <i>Moorella caeni</i>

Moorella species are thermophilic acetogens that primarily produce acetate from one-carbon (C1) compounds including CO, CO₂ (+H₂), methanol and formate. Notably, Moorella caeni DSM 21394^T displays a hydrogenogenic metabolism on CO and an acetogenic metabolism on methanol. Furthermore, M. caeni is unable to use CO₂ (+H₂) and grows only on formate in the presence of a methanogen or when thiosulfate is added as an electron acceptor. Presently, all theoretical frameworks for C1 metabolism in Moorella species are derived from experimental and genomic analyses of Moorella thermoacetica, which exhibits an acetogenic metabolism with all C1 substrates. In this study, we applied a transcriptomics approach to elucidate the mechanisms underlying the C1 metabolism of Moorella caeni during growth on methanol and CO. Our results indicate that respiratory Complex 1, a proton-translocating (ubi)quinone oxidoreductase, is the primary respiratory enzyme in methanol-grown cells of M. caeni. Conversely, in CO-grown cells, an energy-conserving hydrogenase complex (Ech) appears to be the primary respiratory complex, alongside respiratory Complex 1. This study provides insight into the C1 metabolism of M. caeni and reveals variations in gene syntenies related to C1 metabolism among the Moorella genus.