Abstract: Nine high molecular weight (HMW) PAH degrading bacteria were isolated from PAH contaminated soil of a coking plant site using the enrichment procedure and detection of polycyclic aromatic hydrocarbon dioxygenase gene. The degradation ability of HMW-PAHs was examined in flasks with pyrene as carbon source. The results showed that strains J6, S5, S4, S2 and B4 had stronger degradation ability for pyrene. After 21 days, the degradation rates of pyrene in all treatments were higher than 55%. The degradation rate of pyrene in B4 treatment was the highest, reaching 70.2%. We further analyzed the degradation ability of five strains and their mixture in pyrenecontaminated soil. Results showed that the degradation rate of pyrene in the treatment inoculating mixed bacteria were higher than that inoculating single bacterium. Among them, the treatments H4 (mixture) and B4 had better degradation rate of pyrene, and the degradation rates of pyrene reached 29.3% and 18.3% after 49 d, respectively. J6, S5, S4, S2 and B4 were identified as Rhodococcus ruber, Bacillus sp.,Sphingopyxissp., Sphingopyxissp. and Pseudomonas sp. respectively based on sequence analysis of 16S rRNA. The abundance and activity of microorganisms in the H4 and B4 treatments under electric field conditions were significantly increased, and the degradation rates of pyrene were 32.9% and 20.1% higher than those without electric field conditions. This indicated that  five strains of HMW-PAH degrading bacteria had strong electric field adaptability and could be applied in the electro bioremediation of HMW-PAHs contaminated soil.

Key words: water, allometry., biomass allocation, clipping, nutrient