Isolation of Chrysene Degrading Bacteria from Soils of Pars Special Economic Energy Zone (Assaluyeh) and Investigating Chrysene Removal by Them

Polycyclic aromatic hydrocarbons due to their toxicity, carcinogenicity, and resistant to bacterial degradation are considered as one of the important environmental threatening factors. Chrysene is an aromatic compound with four rings. In this research chrysene degrading bacteria were isolated from oil contaminated soils in pars special economic energy zone. Degradation of chrysene in laboratory condition and the effect of different chrysene concentration on bacterial growth were investigated. After filtration of samples they were cultivated in culture medium containing inorganic compounds and chrysene and then incubated at 32°C for two weeks. Isolated bacteria were identified by common microbiological and biochemical tests. The rate of bacterial growth was evaluated by measuring optical density (OD 600) in presence of 0.1-0.4 g/l chrysene. Degradation and removal rate of chrysene by isolated bacteria was investigated using chromatography machine. Four bacterial species; Pseudomonas putida, Mycobacterium sp, micrococcus varians and Bacillus coagulans were isolated and identified. Pseudomonas putida was the strongest bacteria for chrysene degradation. The bacterium grew in minimum possible time and its optical density was higher than other bacteria for all the concentrations tested. This bacterium degraded and removed 95% of chrysene with primary concentration of 0.1 g/l during 10 days. Mycobacterium sp was the second strongest bacterium for chrysene degradation. The weakest bacterium in chrysene degradation was Bacillus coagulans that degraded 42% of chrysene after 10 days. Pseudomonas putida had the highest optical density and degradation ability for chrysene. Due to different reasons such as presence at different environmental conditions and having degrading enzymes this bacterium has the ability to degrade and remove polycyclic aromatic hydrocarbons.