The alkane hydroxylase gene of Burkholderia cepacia RR10 is under catabolite repression control

In many microorganisms the first step for alkane degradation is the termina l oxidation of the molecule by an alkane hydroxylase. We report the charact erization of a gene coding for an alkane hydroxylase in a Burkholderia cepa cia strain isolated from an oil-contaminated site. The protein encoded show ed similarity to other known or predicted bacterial alkane hydroxylases, al though it clustered on a separate branch together with the predicted alkane hydroxylase of a Mycobacterium tuberculosis strain. Introduction of the cl oned B. cepacia gene into an alkane hydroxylase knockout mutant of Pseudomo nas fluorescens CHAO restored its ability to grow on alkanes, which confirm s that the gene analyzed encodes a functional alkane hydroxylase. The gene, which was named alkB, is not linked to other genes of the alkane oxidation pathway. Its promoter was identified, and its expression was analyzed unde r different growth conditions. Transcription was induced by alkanes of chai n lengths containing 12 to at least 30 carbon atoms as well as by alkanols. Although the gene was efficiently expressed during exponential growth, tra nscription increased about fivefold when cells approached stationary phase, a characteristic not shared by the few alkane degraders whose regulation h as been studied. Expression of the alkB gene was under carbon catabolite re pression when cells were cultured in the presence of several organic acids and sugars or in a complex (rich) medium. The catabolic repression process showed several characteristics that are clearly different from what has bee n observed in other alkane degradation pathways.