Abstract: Microbial degradation is a feasible treatment technology for the remediation of PAHscontaminated soils, but its effect depends on many factors including the metabolic activity of microorganisms and the bioavailability of PAHs in  contaminated soils. Many researches have focused on the microbes that can degrade high molecular weight (HMW) PAHs. In this paper, a filamentous fungus Paecilomyces variotii was isolated and purified from a heavy oil contaminated soil, and its capability in degrading HMW PAHs Benzo ［a］ anthracene (BaA), benzo ［a］pyrene (BaP), benzo［b］fluoranthene (BbF), benzo ［k］ fluoranthene (BkF), and indeno ［1,2,3-cd］ pyrene (IcdP) was examined with liquid culture. After 30 days inoculation with P. variotii, the degradation rate of test PAHs was 16.1%-24.6% in mixed system and 10.4%-33.3% in single system, and there was a definite difference in the degradability of test PAHs in the two systems. In single system, the degradation rate of benzo［k］fluoranthene and benzo［b］fluoranthene increased, while the other PAHs were in adverse. The findings of this study could provide a new germplasm resource in the researches of the co-metabolism mechanisms of HMW PAHs and the bioremediation of soil-water environment contaminated by compound PAHs.

Key words: Mixed rare earth elements, Yellow cinnamon soil, Soil microbes, Low dosage accumulation, EC₅₀