Isolation of Polycyclic Aromatic Hydrocarbon Degrading Bacterial Strains Isolated from Indigenous Microbial Communities of Petroleum Contaminated Soils

Soil and sludge samples polluted with petroleum waste from Cairo Oil Refining Company Mostorod, Qalyubia, Egypt for more than 41 years were used for isolation of indigenous microbial communities. These communities were grown on seven polycyclic aromatic hydrocarbon compounds (naphthalene(Naph.), phenanthrene (Phen.), anthracene (Anth.), fluorancene (Flu.), acenaphthene (Acen.), pyrene (Pyr.) and benzo-aanthracene (B-a-Anth.)) as a sole carbon and energy source. The growth of the seven different bacterial communities on the seven different PAHs had been investigated by recording their growth (O.D) and secretion of extracellular protein at zero time (initial) and after 7, 15, 21 and 28 days incubation. The growth of community (1) on 50 mg/L Naph was 5.0, 10.0, 9.5 and 8.6 times the initial after 7, 15, 21 and 28 days, respectively. The same, community (1) gave the best growth on 250 mg/L Phen. (2.8, 2.7, 4.6 and 6.4 times the initial) after 7, 15, 21 and 28 days, respectively. The ability of community (1) to grow on 50.0, 100, 10.0 mg/L of Anth. Acen. and Flu. respectively and 100 μg/L for both of Pyr. and B-a-Anth. have been recorded also. The results revealed that community (1) gave the best growth and extracellular protein secretion followed by community (2). Count of these seven communities after 28 days incubation revealed an increase in bacterial count ranging from 0.8-1.0 ; 0.9-1.3 ; 0.91.2 ;0.7 -1.0 ; 0.9-1.2 ; 0.9-1.3 and 0.6-1.2 log cycles on Naph. Phen. Anth. Flu. Acen. Pyr. And B-aAnth. respectively. The highest total bacterial count at zero time (initial) was 1.6 x 10 CFU/ml for community (4), 7 while the highest hydrocarbon degrading bacterial (HDB) count was 3.0 x 10 CFU/ml for community (3). Six 5 isolates (MAM-26, 29, 43, 62, 68, 78) were able to grow on different concentrations of five chosen PAHs (Naph. Phen. Anth. Pyr. and B-a-Anth). The most promising bacterial strain MAM-62 has been exposed to different doses of gamma radiation. As the dose of radiation increased, the viable count of MAM-62decreased. Dose of 15 KGy reduced the viable count by 7.25 log cycles.