Adaptations of aquatic microorganisms to the biodegradation of oil sands hydrocarbons of the Athabasca

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Microorganisms, including bacteria, fungi and yeast from sediments of the major rivers of the Athabasca oil sands formation were found to be capable of growth on Athabasca bitumen as sole source of carbon and energy. During bitumen biodegradation, which proceeds very slowly, the saturate and aromatic hydrocarbon fractions of the bitumen were depleted. At the sediment-water interface of these rivers an active, heterotrophic community of microorganisms was enumerated. Numbers by direct count and activity assessed by 14 C-glutamate heterotrophic potential were not greater in sediments containing eroded bituminous hydrocarbons than in control sediments from outside the oil sands formation. There was also no difference in the MPN of 14 C-hexadecane or 14 C-naphthalene degrading microorganisms in oil sands sediments relative to controls. Bitumen degrading microorganisms enumerated by plate count were enriched in bitumen-containing sediments, although there was a surprising general capability for growth on bituminous hydrocarbons at all sites. The rate of assimilation and respiration of 14 C-hexadecane and 14 C-naphthalene carried within bitumen adsorbed to silica gel was significantly greater at oil sands sites than at control sites. These results indicated an adaptation of microorganisms to the problems of colonization and mobilization of hydrocarbons in a bituminous hydrocarbon substrate. There were marked seasonal fluctuations in heterotrophic activity and hydrocarbon biodegradation potentials. There was also a dependence of hydrocarbon biodegradation determined with radiolabeled substrates and by mass loss on the availability of nutrient nitrogen and phosphorus. Trace organic additions did not alter the rate; however, glucose addition caused sparing of the hydrocarbon substrates. 14 C-Naphthalene was degraded at a greater rate in sediment samples and its biodegradation was less sensitive to nutrient limitations than 14 C-hexadecane. Embedding and transmission electron microscopy of bitumen surfaces colonized 1n situ indicated a polysaccharide mediated adhesion of microorganisms to the hydrocarbon surface. Other microorganisms were 1n direct contact with the bitumen with no extracellular polymer involved. Channeling within the substrate was one strategy used to increase the surface area available for colonization. Characterization of bitumen degrading isolates indicated Pseudomonas, Xanthomonas, Acinetobacter, Nocardia species and coryneforms were capable of growth on the saturate and aromatic components of bitumen. Most of these isolates were also able to grow on simple n-alkanes and this approach was taken in order to obtain cell yields sufficient for investigating possible oxygenases involved in bitumen biodegradation. Cytochrome P450, a known hydrocarbon oxidizing hemoprotein with a broad substrate specificity, was found in Acinetobacter species from sediments of the Athabasca. The implications of these findings for microorganisms involved in heavy oil biodegradation are discussed.
Bibliography: p. 206-243.
Wyndham, R. C. (1981). Adaptations of aquatic microorganisms to the biodegradation of oil sands hydrocarbons of the Athabasca (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/21925