An experimental study was undertaken to assess the efficiency of Pseudomonas aeruginosa, Bacillus subtilis, and Acinetobacter lwoffi isolated from petroleum contaminated water and soil samples to degrade crude oil, separately and in a mixed bacterial consortium. Capillary gas chromatography was used for testing the effect of those bacterial species on the biodegradation of crude oil. Individual bacterial cultures showed less growth and degradation than did the mixed bacterial consortium. At temperature 22°C, the mixed bacterial consortium degraded a maximum of 88.5% of Egyptian crude oil after 28 days of incubation. This was followed by 77.8% by Pseudomonas aeruginosa, 76.7% by Bacillus subtilis, and 74.3% by Acinetobacter lwoffi. The results demonstrated that the selected bacterial isolates could be effective in biodegradation of oil spills individually and showed better biodegradation abilities when they are used together in mixed consortium. 1. Introduction Oil spillage and oil pollution in water environment have been a major threat to the ecosystem and human being through the transfer of toxic organic materials including polycyclic aromatic hydrocarbons (PAHs) into the food chain [1]. Presence of polycyclic aromatic hydrocarbons (PAHs) in soil and water is major problem as environmental contaminants and most of these PAHs are recalcitrant in nature. Physical and chemical methods like volatilization, photooxidation, chemical oxidation, and bioaccumulation [2] are rarely successful in rapid removal and cleaning up PAHs [3], and also these methods are not safe and cost effective when compared to microbial bioremediation. Bacteria have long been considered as one of the predominant hydrocarbon degrading agents found in the environment, which are free living and ubiquitous [4]. Petroleum hydrocarbons are important energy resources used by industry and in our daily life. At the same time, petroleum is a major pollutant of the environment [5]. Due to its complicated composition, petroleum has the potential to elicit multiple types of toxic effects. It can cause acute lethal toxicity, sub-lethal chronic toxicity, or both depending on the exposure, dosage, and the organism exposed. Some components of petroleum have the potential to bioaccumulate within susceptible aquatic organisms and can be passed by trophic transfer to other levels of the food chain [6, 7]. The success of bioremediation technologies applied to hydrocarbon-polluted environments highly depends on the biodegrading capabilities of native microbial populations or exogenous microorganisms used
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