Biodegradability and crude oil composition

Four crude oils (Prudhoe Bay, Norman Wells, Atkinson Point, and Lost Horse Hill) of different chemical composition were tested as to their biodegradability under mesophilic and psychrophilic conditions. Changes in bacterial numbers and chemical composition of the oils were monitored using a plate count and chromatographic technique respectively. Populations induced under psychrophilic conditions readily metabolized similar quality oils under mesophilic conditions. Mesophilic populations, however, only showed a limited metabolic capability on similar quality oils under psychrophilic conditions. Gram-negative rods were predominant in all the populations obtained under these experimental conditions. The ability of the mixed populations to use crude oil as a sole carbon source was dependent not only on the composition and amount of the n-saturate fraction but also on that of the asphaltene and NSO (i.e. nitrogen-, sulfur-, and oxygen-containing) fraction. Growth on an oil which lacked a normal n-alkane component indicated that the aromatic fraction of oil was capable of sustaining bacterial growth. Oil quality and temperature of incubation affected the generic composition of populations obtained which would use crude oil. The isoprenoids, phytane and pristane, while readily used under mesophilic conditions, were more resistant to bacterial metabolism under psychrophilic conditions.