Optimization of Crude Oil Biodegradation by Acinetobacter Calcoacticus BS and Pseudomonas Aeroginosa AS Isolated from Persian Gulf

Oil pollution in marine environments is a global problem. Annually, large amounts of oil are released to marine environments. Persian Gulf is a strategic place where approximately 60 % of oil transfer takes place. In order to isolate crude oil degrading bacteria, coastal sand and sea water samples were collected from different zones in Persian Gulf. Crude oil degrading bacteria were then screened in selective media and strains, which showed high growth rate and crude oil removal, and selected for further study. These strains were identified by biochemical and molecular methods. The results showed that these strains belonged to Acinetobacter and Pesudomonas genus. Experiments were designed using Taguchi method by selecting six factors including temperature, nitrogen source, oil concentration, carbon source and degradative bacterium. Five factors had three levels and one (temperature) had two levels and thus L18 experiments were carried out. The results obtained from Taguchi experiments showed that temperature has no effect on biodegradation, although biodegradation can occur between 30-37 °C. (NH4)2SO4 had the best effect on biodegradation among nitrogen sources. The rate of biodegradation in the presence of a chemical surfactant is greater than that in the absence of one and of the two surfactants used in this study tween 80 was more effective. Biodegradation dramatically decreased when the concentration of crude oil increased from 1 to 4 %. When an additional carbon source was used, the rate of biodegradation increased. Mixed culture and A. calcoaceticus strain BS had the same effect on biodegradation but both levels were greater than P. aeruginosa AS. All factors have 95.3 % contributions and the remaining 4.7 % percent was the experimental error. Efficiency of Taguchi design was 77 %. By using the strains obtained in this investigation and future assessment of the efficiency of these strains on saline water, oil contamination in Persian Gulf can be reduced.