Microbial degradation of aromatics and saturates in Prudhoe Bay crude oil as determined by glass capillary gas chromatography

Abstract

Water samples obtained from three different marine environments (including a commercial harbor, a pristine area, and an oil tanker dock area) from the coast of Washington State were challenged with Prudhoe Bay crude oil under shake-flask conditions at 8 degrees C. Replicate cultures were grown with and without nitrogen (NO3-, NH4+) and phosphate supplementation. After varying incubation periods, the residual oil was extracted and separated on silica gel columns into saturate aromatic fractions and these were analyzed by glass capillary gas chromatography to detect the degradation of various compounds. After 27 days of incubation, both the aromatic and saturate fractions were extensively degraded by the microorganisms from these environments when supplemented with nitrogen and phosphorus. Without nutrient supplementation, the aromatics were more readily attacked than the saturates by the populations from the pristine environment and from the commercial harbor area. Under these limited nutrient conditions, samples from near oil tanker docks showed moderate degradation of both the saturate and aromatic fractions. Time course studies, using nutrient-supplemented marine samples, showed that the simple aromatics (e.g., naphthalene and 2-methylnaphthalene) were more readily degraded than the n-alkanes. However, once the breakdown of these saturates commenced, these were quickly removed from the oil. The aromatic degradation continued to progress from lower molecular weight, less complex molecules to larger, more complex molecules in the approximate series C2 naphthalenes; phenanthrene and dibenzothiophene; C3 naphthalenes and methylphenathrenes; C2 phenanthrenes.