Biodegradation of oil spills and fuel contaminated soils by Streptomyces isolates

         Five soil samples (contaminated with oil spills for many years) were collected from different places in Baghdad. From these samples, fourteen isolates were obtained as a preliminary degraders for hydrocarbons. The isolates were recultured in the mineral salt medium supplemented with crude oil and diesel, separately, to ensure their degradation ability. Despite that with 5 isolates S7, S8, S11, S12, and S14 gave good degradation activity, but isolates S7 and S14 were the most efficient due to their highest , degradation ability for crude oil and diesel as a sole source of carbon.
       The two isolates were identified depending on their morphological, cultural, and biochemical characteristics. Results showed that they were belonged to Streptomyces by their ability to use various pure sources of hydrocarbons. Isolate S7 was superior growth comparing with S14 isolate in (Hexadecane, Tetrahydrofuran, Anthracene, and Naphthalene). Optimum conditions for degradation of crude oil and diesel by S7 and S14 isolates were investigated. By growing them in the modified yeast extract malt extract media  in different range of pHs, temperatures, agitation, and salt concentrations  with addition of 1% crude oil and diesel  ,separately, after incubation for 10 days. Isolation and purification of biosurfactants produced by Streptomyces using acid precipitation method yielded (0.5, 1) g/L of biosurfactant from S7 and S14 isolates, respectively. The biochemical detection tests and Fourier Transformed Infrared spectroscopy analysis indicated the lipopeptide nature of biosurfactants.
         Gas chromatography analysis for liquid-liquid extraction of residual crude oil and diesel showed significant differences in the composition at the end of the experiment. Most of long and complex carbon chains were broken in to simpler types, and disappearance of some compounds was observed during the process. When the plasmid profile for S7 and S14 isolates were studied, results
showed that these isolates harbored small plasmid DNA bands. In order to study the role of its plasmid in degradation of hydrocarbons, curing experiment was performed by using low pH curing method. Results in this regard the plasmid DNA has no role in the biodegradation since both isolates ability in degradation of the hydrocarbon.