ISOLATION AND CHARACTERIZATION OF CRUDE OIL-DEGRADING BACTERIA FROM PETROLEUM OIL CONTAMINATED EGYPTIAN SOILS

Eleven bacterial strains were isolated from two different oil contaminated Egyptian soils. They were characterized according to their phenotypic examination as species of the genus Bacillus. These bacterial populations showed counts ranging between 8 and 10 log CFU/g soil on the agar plates. An experimental study was undertaken to assess the efficiency of these bacterial isolates in degradation of the petroleum oil in their culture medium amended with 1% v/v petroleum oil. Results revealed that both CS1.1 and CS1.7 are the most effective isolates to degrade two crude oils from Suez and Agiba Company for the first time by growing the individual isolates separately on oil agar media. In addition, CS1.1and CS1.7 exhibited 55.6% and 53.5%, respectively emulsification activity after 48 hrs. incubation time. Also, isolates CS1.1 and CS1.7 could reduce the surface tension to 36.5 ± 0.25mN/m and 37.5 ± 0.45mN/m, respectively in less than 12 hrs. in glucose based media. The gravimetric analysis revealed that both CS1.1 and CS1.7 isolates were able to degrade the petroleum oil and utilize it as a sole carbon source for growth, energy and reproduction. These isolates, CS1.1 and CS1.7 degraded 65% and 64 % of added petroleum oil respectively, over 15 days incubation time. Also, the change in absorbance values of the tested samples from 0.936 O.D. to 1.832 O.D. compared with the control sample 0.815 O.D. indicates the breakdown of the molecular structure of oil and confirms the degradation of crude oil by bacterial isolates. Physiological and biochemical parameters for those the most potent degrading isolates were determined. They were identified as Bacillus subtilis and Bacillus licheniformis.