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Applied and Environmental Microbiology, July 1999, p. 2961-2968, Vol. 65, No. 7
0099-2240/99/$04.00+0

Physiological Adaptations Involved in Alkane Assimilation at a Low Temperature by Rhodococcus sp. Strain Q15dagger

L. G. Whyte,1,* S. J. Slagman,1 F. Pietrantonio,1 L. Bourbonnière,1 S. F. Koval,2 J. R. Lawrence,3 W. E. Inniss,4 and C. W. Greer1

NRC-Biotechnology Research Institute, Montreal, Quebec, Canada H4P 2R21; University of Western Ontario, London, Ontario, Canada N6A 5C12; National Water Research Institute, Environment Canada, Saskatoon, Saskatchewan, Canada S7N 3H5,3 and University of Waterloo, Waterloo, Ontario, Canada N2L 3G14

Received 5 January 1999/Accepted 20 April 1999

We examined physiological adaptations which allow the psychrotroph Rhodococcus sp. strain Q15 to assimilate alkanes at a low temperature (alkanes are contaminants which are generally insoluble and/or solid at low temperatures). During growth at 5°C on hexadecane or diesel fuel, strain Q15 produced a cell surface-associated biosurfactant(s) and, compared to glucose-acetate-grown cells, exhibited increased cell surface hydrophobicity. A transmission electron microscopy examination of strain Q15 grown at 5°C revealed the presence of intracellular electron-transparent inclusions and flocs of cells connected by an extracellular polymeric substance (EPS) when cells were grown on a hydrocarbon and morphological differences between the EPS of glucose-acetate-grown and diesel fuel-grown cells. A lectin binding analysis performed by using confocal scanning laser microscopy (CSLM) showed that the EPS contained a complex mixture of glycoconjugates, depending on both the growth temperature and the carbon source. Two glycoconjugates [beta -D-Gal-(1-3)-D-GlcNAc and alpha -L-fucose] were detected only on the surfaces of cells grown on diesel fuel at 5°C. Using scanning electron microscopy, we observed strain Q15 cells on the surfaces of octacosane crystals, and using CSLM, we observed strain Q15 cells covering the surfaces of diesel fuel microdroplets; these findings indicate that this organism assimilates both solid and liquid alkane substrates at a low temperature by adhering to the alkane phase. Membrane fatty acid analysis demonstrated that strain Q15 adapted to growth at a low temperature by decreasing the degree of saturation of membrane lipid fatty acids, but it did so to a lesser extent when it was grown on hydrocarbons at 5°C; these findings suggest that strain Q15 modulates membrane fluidity in response to the counteracting influences of low temperature and hydrocarbon toxicity.

* Corresponding author. Mailing address: NRC-Biotechnology Research Institute, 6100 Royalmount Ave., Montreal, Quebec, Canada H4P 2R2. Phone: (514) 496-6316. Fax: (514) 496-6265. E-mail: Lyle.Whyte{at}nrc.ca.

dagger Publication 41842 of the National Research Council Canada.

Applied and Environmental Microbiology, July 1999, p. 2961-2968, Vol. 65, No. 7
0099-2240/99/$04.00+0


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