Expression of an alcohol dehydrogenase gene in a heterotrophic bacterium induces carbon dioxide-dependent high-yield growth under oligotrophic conditions

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 CO -dependent and accompanied with CO incorporation. In the HYGO mutant, a transposon was inserted just upstream of the putative Zn-dependent alcohol dehydrogenase (ADH) gene ( ) so that the gene was constitutively expressed, probably by the transposon-derived promoter. The -deletion mutant (UT26DAX) harbouring a plasmid carrying the 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 was highly expressed in these HYGO mutants, while no HYGO mutant appeared among UT26DAX-derived hypermutator strain cells, indicating the necessity of for the HYGO phenotype. His-tagged AdhX that was expressed in and purified to homogeneity showed ADH activity towards methanol and other alcohols. Mutagenesis analysis of the gene indicated a correlation between the ADH activity and the HYGO phenotype. These results demonstrated that the constitutive expression of an -encoding protein with ADH activity in UT26 leads to the CO -dependent HYGO phenotype. Identical or nearly identical orthologues were found in other sphingomonad strains, and most of them were located on plasmids, suggesting that the -mediated HYGO phenotype may be an important adaptation strategy to oligotrophic environments among sphingomonads.