Isolation and optimization of PAH-degradative bacteria from contaminated soil for PAHs bioremediation

The objective of the present study is to isolate PAH-degradative bacteria from petroleum-contaminated soils and to optimize their degradative conditions including pH, glucose, nitrogen and phenanthrene concentrations required for bioremediation purposes. Several bacterial strains were isolated through enrichment and one strain, Burkholderia cocovenenans (BU-3) that was tentatively identified by the Biolog system, demonstrated a high removal rate of phenanthrene over other strains. More than 95% in 100 and 500 mg L^-1 and 65% in 1000 mg L^-1 of phenanthrene contents was reduced in the culture media, respectively. Maximum rate of phenanthrene removal up to 4.2 mg hr^-1 occurred in the culture containing 1000 mg L^-1 phenanthrene. Media at a pH between 6.5 to 7.0 were more favorable for the degradation of phenanthrene by BU-3. Although increasing glucose concentrations from 0.45 to 3 g L^-1 resulted in a better bacterial growth of the isolated bacteria, the degradation of phenanthrene was reduced significantly. Nitrogen supplement did not exert a significant effect on bacterial growth and phenanthrene degradation. The isolated Burkholderia cocovenenans BU-3 demonstrated to be a feasible strain for degradation of phenanthrene at a neutral pH, even up to a phenanthrene concentration of 1000 mg L^-1.