1. Expression of an alcohol dehydrogenase gene in a heterotrophic bacterium induces carbon dioxide-dependent high-yield growth under oligotrophic conditions
- Author
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Masataka Tsuda, Takayuki Horiuchi, Shinnosuke Inaba, Hironori Sakai, Hiromi Kato, Hirokazu Yano, Yuji Nagata, and Yoshiyuki Ohtsubo
- Subjects
Transposable element ,Mutant ,Mutagenesis (molecular biology technique) ,medicine.disease_cause ,Microbiology ,03 medical and health sciences ,Plasmid ,Bacterial Proteins ,medicine ,Promoter Regions, Genetic ,Gene ,Escherichia coli ,030304 developmental biology ,Alcohol dehydrogenase ,0303 health sciences ,biology ,030306 microbiology ,Chemistry ,Alcohol Dehydrogenase ,Heterotrophic Processes ,Gene Expression Regulation, Bacterial ,Carbon Dioxide ,Molecular biology ,Phenotype ,Sphingomonadaceae ,Mutation ,biology.protein ,Hexachlorocyclohexane ,Plasmids - Abstract
Sphingobium japonicum strain UT26, whose γ-hexachlorocyclohexane-degrading ability has been studied in detail, is a typical aerobic and heterotrophic bacterium that needs organic carbon sources for its growth, and cannot grow on a minimal salt agar medium prepared without adding any organic carbon sources. Here, we isolated a mutant of UT26 with the ability to grow to visible state on such an oligotrophic medium from a transposon-induced mutant library. This high-yield growth under oligotrophic conditions (HYGO) phenotype was CO2-dependent and accompanied with CO2 incorporation. In the HYGO mutant, a transposon was inserted just upstream of the putative Zn-dependent alcohol dehydrogenase (ADH) gene (adhX) so that the adhX gene was constitutively expressed, probably by the transposon-derived promoter. The adhX-deletion mutant (UT26DAX) harbouring a plasmid carrying the adhX gene under the control of a constitutive promoter exhibited the HYGO phenotype. Moreover, the HYGO mutants spontaneously emerged among the UT26-derived hypermutator strain cells, and adhX was highly expressed in these HYGO mutants, while no HYGO mutant appeared among UT26DAX-derived hypermutator strain cells, indicating the necessity of adhX for the HYGO phenotype. His-tagged AdhX that was expressed in Escherichia coli and purified to homogeneity showed ADH activity towards methanol and other alcohols. Mutagenesis analysis of the adhX gene indicated a correlation between the ADH activity and the HYGO phenotype. These results demonstrated that the constitutive expression of an adhX-encoding protein with ADH activity in UT26 leads to the CO2-dependent HYGO phenotype. Identical or nearly identical adhX orthologues were found in other sphingomonad strains, and most of them were located on plasmids, suggesting that the adhX-mediated HYGO phenotype may be an important adaptation strategy to oligotrophic environments among sphingomonads.
- Published
- 2020