Lanthanides (Ln) are an essential cofactor for XoxF-type methanol dehydrogenases (MDHs) in Gram-negative methylotrophs. The Ln dependency of XoxF has expanded knowledge and raised new questions in methylotrophy, including the differences in characteristics of XoxF-type MDHs, their regulation, and the methylotrophic metabolism including formaldehyde oxidation. In this study, we genetically identified one set of Ln- and Ca-dependent MDHs (XoxF1 and MxaFI), that are involved in methylotrophy, and an ExaF-type Ln-dependent ethanol dehydrogenase, among six MDH-like genes in strain 22A. We also identified the causative mutations in MxbD, a sensor kinase necessary for expression and repression, for suppressive phenotypes in mutants defective in methanol growth even in the absence of Ln. Furthermore, we examined the phenotypes of a series of formaldehyde oxidation-pathway mutants (, , in the tetrahydromethanopterin (HMPT) pathway and in the glutathione-dependent formaldehyde dehydrogenase (GSH) pathway). We found that MxaF produces formaldehyde to a toxic level in the absence of the formaldehyde oxidation pathways and that either XoxF1 or ExaF can oxidize formaldehyde to alleviate formaldehyde toxicity in vivo. Furthermore, the GSH pathway has a supportive role for the net formaldehyde oxidation in addition to the HMPT pathway that has primary importance. Studies on methylotrophy in species have a long history, and this study provides further insights into genetic and physiological diversity and the differences in methylotrophy within the plant-colonizing methylotrophs.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7356819PMC
http://dx.doi.org/10.3390/microorganisms8060822DOI Listing

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