In the present work we have studied growth optimization of previously isolated diesel oil degrading Bacillus sp. i.e. Bacillus coagulans 1A, Bacillus cereus 3E, Bacillus subtilis 4F and Bacillus megaterium 4H from petroleum contaminated soil of Barmer, Rajasthan at different concentrations of diesel oil and at various pH and temperature. Analysis of extracted diesel oil from bacterial cultures was done gravimetrically and through GC-MS technique. The results of the study reveals that optimum hydrocarbon degrading activity of all the four bacterial isolates 1A, 3E, 4F and 4H was found at pH 7 and 37⁰C. After an incubation period of 7 days at 37⁰C biodegradation rates of 7.84%± 3.57%, 12.34% ± 2.9%, 29.79% ± 3.83% and 7.52% ± 2.8% were found for Strain 1A, 3E, 4F and 4H respectively, while biodegradation rates after an incubation of 15 days were found increased i.e. 60.00% ± .02%, 67.44% ± 4.5%, 82.39% ± 5.1% and 49.00% ± 4.8% for strains 1A, 3E, 4F and 4H respectively. Thus, the results obtained clearly shows that isolated strain Bacillus cereus 3E and Bacillus subtilis had degraded 4F was degraded more than 65% and 80% of diesel oil. Strain Bacillus megaterium 4H was found degrading less than 50% of diesel oil. GC-MS chromatogram showed reduction in the intensity of diesel oil peaks after the degradation with strains 1A, 3E, 4F and 4H. Therefore this study proved that the strain Bacillus cereus3E and strain Bacillus subtilis4F is the most potent diesel oil degrader among all four isolates.
