Microbial degradation of organic sulfur compounds in Prudhoe Bay crude oil

Water samples from three different marine environments in Washington State were challenged with Prudhoe Bay crude oil and incubated at 8 °C with aeration. Some cultures were supplemented with NH4NO3 and phosphate and after various lengths of time, up to 27 days, the residual oil was extracted and fractionated using silica gel columns. The aromatic fraction was analyzed by capillary gas chromatography using a sulfur-specific flame photometric detector. The oil contained alkylbenzo[b]thiophenes, dibenzothiophene, and C1- and C2-dibenzothiophenes and the degradation of these was monitored. Many of the sulfur heterocycles were metabolized without nutrient supplementation although the number and extent of the compounds degraded increased with nutrient addition. The order of susceptibility of the sulfur heterocycles in homologous series was found to be the following: C2-benzo[b]thiophenes > C3-benzothiophenes; dibenzothiophene > C1-dibenzothiophenes > C2-dibenzothiophenes. With nutrient supplementation, the microbial population from a harbor area metabolized the sulfur compounds more readily than those from near an oil tanker dock or from a pristine state park beach. Without supplementation, the population from the tanker dock area degraded many fewer sulfur heterocycles than the other two populations.