BIODEGRADATION OF VARIABLE-CHAIN-LENGTH ALKANES AT LOW-TEMPERATURES BY A PSYCHROTROPHIC RHODOCOCCUS SP

The psychrotroph Rhodococcus sp. strain Q15 was examined for its abili ty to degrade individual n-alkanes and diesel fuel at low temperatures , and its alkane catabolic pathway was investigated by biochemical and genetic techniques. At 0 and 5 degrees C, Q15 mineralized the short-c hain alkanes dodecane and hexadecane to a greater extent than that obs erved for the long-chain alkanes octacosane and dotriacontane. Q15 uti lized a broad range of aliphatics (C-10 to C-21 alkanes, branched alka nes, and a substituted cyclohexane) present in diesel fuel at 5 degree s C. Mineralization of hexadecane at 5 degrees C was significantly gre ater in both hydrocarbon contaminated and pristine soil microcosms see ded with Q15 cells than in uninoculated Control soil microcosms. The d etection of hexadecane and dodecane metabolic intermediates (1-hexadec anol and 2-hexadecanol and 1-dodecanol and 2-dodecanone, respectively) by solid phase microextraction-gas chromatography-mass spectrometry a nd the utilization of potential metabolic intermediates indicated that Q15 oxidizes alkanes by both the terminal oxidation pathway and the s ubterminal oxidation pathway. Genetic characterization by PCR and nucl eotide sequence analysis indicated that Q15 possesses an aliphatic ald ehyde dehydrogenase gene highly homologous to the Rhodococcus erythrop olis thcA gene. Rhodococcus sp. strain Q15 possessed two large plasmid s of approximately 90 and 115 kb (shown to mediate Cd resistance) whic h were not required for alkane mineralization, although the 90-kb plas mid enhanced mineralization of some alkanes and growth on diesel oil a t both 5 and 25 degrees C.