A simple and rapid method (slow-stirring method) for extracting environmental DNA (eDNA) from soils was constructed by physical mild stirring with chemical treatment. eDNA was extracted efficiently with minimal damage from various kinds of soil. The amount of eDNA and soil bacterial biomass showed a linear proportional relation [Y=(1.70x10(8))X, r2=0.96], indicating that bacterial biomass could be evaluated by quantifying levels of eDNA. Consequently, the average bacterial biomass in an agricultural field was calculated as 5.95x10(9) cells/g sample, approximately 10-100 times higher than that in non- and oil-polluted fields.

-The safety of an oil-degrading bacterium, C2 strain, was evaluated for utilization in an open system for bioremediation of oil-contaminated environments. The C2 strain was identified as Rhodococcus erythropolis by performing an alignment analysis of the whole 16S rRNA sequence. R. erythropolis was classified as a nonpathogenic (category 1) bacterium. Biological and biochemical properties of the C2 strain also confirmed its nonpathogenicity. The pathogenicity and basic ecotoxicity were studied in laboratory animals and in a variety of test species, respectively. General and inhalation toxicities were not detected; additionally, there was no evidence of skin irritation, mutagenic potential, eye irritation, skin sensitization, ecotoxicity or notable pathogenicity. The comparison of these results with human exposure levels and previously published data indicates that the C2 strain appears to be safe for utilization in bioremediation of polluted environments, requires no special occupational health precautions during the application process, and has a low environmental impact. This study suggests that the C2 strain could be suitable for bioremediation of oil-contaminated environments.