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

Oligotrophic Gene Expression in Rhodococcus erythropolis N9T-4 under Various Nutrient Conditions

Rhodococcus erythropolis N9T-4 is a super oligotroph that grows on an inorganic basal medium without any additional carbon and nitrogen sources and requires CO₂ for its oligotrophic growth. Previously, we found that two genes, aldA and mnoA, encoding NAD-dependent aliphatic aldehyde dehydrogenase and N,N′-dimethyl-4-nitrosoaniline-dependent methanol dehydrogenase, respectively, were highly upregulated under oligotrophic conditions. In this study, we constructed reporter plasmids containing an enhanced green fluorescent protein gene under aldA or mnoA promoters (pAldA and pMnoA, respectively). Fluorescence analysis of N9T-4 cells with reporter plasmids revealed that tryptone and yeast extract strongly repressed the expression of oligotrophy-connected genes, whereas the effect of casamino acids was moderate. Furthermore, remarkably high expression of aldA and mnoA was observed when the reporter strains were grown in media containing primary alcohols, particularly ethanol. Malic acid repressed ethanol-induced gene expression, suggesting that C2 metabolism is involved in the oligotrophic growth of N9T-4. The regulation of oligotrophic gene expression elucidated in this study could provide appropriate conditions for the production of useful compounds in an oligotrophic microbial process.

Genome evolution related to γ-hexachlorocyclohexane metabolic function in the soil microbial population

γ-Hexachlorocyclohexane (γ-HCH)-degrading strain, Sphingobium sp. TA15, was newly isolated from an experimental field soil from which the archetypal γ-HCH-degrading strain, S. japonicum UT26, was isolated previously. Comparison of the complete genome sequences of these 2 strains revealed that TA15 shares the same basic genome backbone with UT26, but also has the variable regions that are presumed to have changed either from UT26 or from a putative common ancestor. Organization and localization of lin genes of TA15 were different from those of UT26. It was inferred that transposition of IS6100 had played a crucial role in these genome rearrangements. The accumulation of toxic dead-end products in TA15 was lower than in UT26, suggesting that TA15 utilizes γ-HCH more effectively than UT26. These results suggested that genome evolution related to the γ-HCH metabolic function in the soil microbial population is ongoing.