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Yanpirat, Patcha Institute of Plant Science and Resources, Okayama University
Nakatsuji, Yukari Institute of Plant Science and Resources, Okayama University
Hiraga, Shota Institute of Plant Science and Resources, Okayama University
Fujitani, Yoshiko Institute of Plant Science and Resources, Okayama University
Izumi, Terumi Institute of Plant Science and Resources, Okayama University
Masuda, Sachiko Institute of Plant Science and Resources, Okayama University
Mitsui, Ryoji Department of Biochemistry, Faculty of Science, Okayama University of Science
Nakagawa, Tomoyuki The United Graduate School of Agricultural Science, Gifu University
Tani, Akio Institute of Plant Science and Resources, Okayama University
Lanthanides (Ln) are an essential cofactor for XoxF-type methanol dehydrogenases (MDHs) in Gram-negative methylotrophs. The Ln(3+)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(3+)- and Ca2+-dependent MDHs (XoxF1 and MxaFI), that are involved in methylotrophy, and an ExaF-type Ln(3+)-dependent ethanol dehydrogenase, among six MDH-like genes inMethylobacterium aquaticumstrain 22A. We also identified the causative mutations in MxbD, a sensor kinase necessary formxaFexpression andxoxF1repression, for suppressive phenotypes inxoxF1mutants defective in methanol growth even in the absence of Ln(3+). Furthermore, we examined the phenotypes of a series of formaldehyde oxidation-pathway mutants (fae1,fae2,mchin the tetrahydromethanopterin (H4MPT) pathway andhgdin 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 H4MPT pathway that has primary importance. Studies on methylotrophy inMethylobacteriumspecies 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.
© 2020 by the authors.
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