HYBRIDIZATION ANALYSIS OF MICROBIAL DNA FROM FUEL OIL-CONTAMINATED AND NONCONTAMINATED SOIL

The enrichment of several genes (xylE, nahAcd, todC1C2BA, tmoABCDE, al kB) that encode enzymes responsible for key steps in the degradation o f hydrocarbons, and one gene specific to rRNA group I of the genus Pse udomonas, was studied in DNA extracted from a fuel oil-contaminated fi eld site, and in laboratory microcosms (with the exception of alkB). T oluene, ethylbenzene, xylene, and naphthalene concentrations were rela ted to the extent of hybridization of the genes in the field studies. Significant differences were observed in the extent of hybridization o f some of the genes between contaminated and noncontaminated samples. In the microcosm studies, gasoline at rates ranging from 0.5 mg to 125 mg gasoline/g of soil as applied to soils, and the changes in hybridi zation intensity of these genes monitored with time. The lower thresho ld of gene enrichment of these genes in response to gasoline addition was below 0.5 mg/g soil. Small increases were observed at the 0.5-mg e xposure level, but hybridization intensity quickly decreased to levels below detection 6-8 days after addition of the gasoline. A dose-respo nse effect was observed from treatments with gasoline concentrations r anging from 0.5 to 35 mg/g soil. Inhibition by toxic components in gas oline was observed at 75 and 125 mg/g soil levels. Hybridization of th e Pseudomonas group 1 probe to field DNA was not significantly enriche d in the contaminated field site, although these sequences were enrich ed in the microcosm studies. Among the genes tested, xylE was the most sensitive indicator of low levels of fuel oil contamination.