BTEX (benzene, toluene, ethylbenzene and xylenes) compounds are the most frequently encountered subsurface contaminants among the various petroleum hydrocarbons. In this study, a new strain, able to degrade BTEX compounds, was isolated from oil contaminated groundwater. Phylogenetic analysis revealed that the isolated strain was most closely related to Pseudomonas zhaodongensis with 98% 16SrRNA gene sequence similarity. A series of batch experiments were carried out to investigate the ability of the new strain for removing BTEX compounds using single and mixed substrates. The optimized values of pH, temperature, and inorganic nutrients (as percent of BTEX concentration) were 7.6, 28.9
C, and 200%, respectively which were obtained by using the response surface methodology for the biodegradation of BTEX. Results showed that the identified strain was able to completely degrade benzene, toluene, and ethylbenzene in the single substrate batch experiments while m-xylene remained non-degradable. Results of dual-substrate experiments revealed co-metabolism of m-xylene in the presence of benzene and toluene. Dioxygenase was found to be the key enzyme incorporating in the cometabolism of m-xylene. Within the mixed substrate batch experiments all BTEX compounds can be degraded. An increase in the production of cell growth due to the degradation of benzene and toluene accelerated the degradation process of m-xylene in the mixed substrate experiments.

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