Biodegradation of Petroleum Hydrocarbons at Low Temperatures
L.G. WHYTE*a, L. BOURBONNIEREa, S.J. SLAGMANa, F. PIETRANTONIOa, J.R. LAWRENCEb, W.E. INNISSc, and C.W. GREERa
a NRC-Biotechnology Research Institute, 6100 Royalmount Ave. Montreal, Quebec, Canada H4P 2R2
b National Hydrology Research Institute, Environment Canada, Saskatoon, Saskatchewan, Canada S7N 3H5
c University of Waterloo, Waterloo, Ontario, Canada N2L 3G1
In many temperate and cold climates, the bioremediation of sites contaminated with petroleum hydrocarbons is possible, although it is hampered by low ambient temperatures for much of the year. Nevertheless, biodegradation of many of the components of petroleum hydrocarbons by psychrophilic and psychrotrophic microorganisms has been observed at low temperatures (1,2). However, to optimize the biodegradative activity of these microorganisms in contaminated sites, it is essential that we acquire a basic understanding of their physiology and ecology as well as the genetics and biochemistry of their catabolic pathways. These traits are relatively poorly understood in cold-adapted bacteria as compared with mesophilic bacteria. In the present study, the abilities and characteristics of several psychrotrophic bacteria, shown to mineralize a variety of petroleum hydrocarbon components at 5℃, are reviewed. The degradative capacity of Rhodococcus sp. Q15, which grows on and emulsifies Bunker C crude oil, diesel fuel, and alkanes at low temperatures, was demonstrated to be chromosome-mediated by plasmid curing of 2 large plasmids found in Q 15. PCR and DNA sequence analysis revealed that Q 15 possesses an aliphatic aldehyde dehydrogenase gene, located on the Q 15 chromosome, that was highly homologous to R. erythropolis thcA. Possible mechanisms by which this organism adapts to and assimilates alkanes, contaminants which are generally insoluble and/or solid at low temperature, were also investigated. Growth of Q15 at 5℃ on hexadecane or diesel fuel resulted in lower surface tensions of the growth medium, compared with growth on glucose/acetate, indicating that Q 15 produces biosurfactant(s), which is associated with the Q 15 cell envelope. Analysis of membrane fatty acid profiles showed that growth of Q15 cells at 5℃ on hexadecane or diesel increased the degree of saturation of fatty acids compared with cells grown on glucose/acetate, although the degree of saturation observed at 5℃ was always less than that observed during Q15 growth on these substrates at 22℃. Examination by transmission electron microscopy or scanning confocal laser
