[Isolation, identification of a pyrene-degrading Mycobacterium sp. strain TZh51and its characteristics for contaminated soil bioremediation]

Abstract

Objective: To obtain pyrene-degrading microorganism strains, and to use them for bioremediation of polycyclic aromatic hydrocarbons-contaminated soil.

Methods: pyrene-degrading strains were isolated by agar plate subliming method. They were identified based on morphological observation, physiological and biochemical characteristics, and on analysis of their 16S rDNA gene sequence homology. Their ability to degrade PAHs in solid and liquid mineral salt medium, and in PAHs-contaminated soil, was studied by counting their live cells and measuring residual PAHs' quantity by HPLC.

Results: Four pyrene-degrading strains TZh51, TZh52, TG42 and TG52 were isolated. The results indicated that TZh51's ability to degrade PAHs was stronger than the other three strains. TZh51 was identified as Mycobacterium sp.; however, it did not belong to the same species with the reported Mycobacterium sp. strain M11. Our results indicated that the effects on maximal pyrene-degrading quantity were incubation temperature at 35 degrees C and pyrene film thickness for 130 ng/mm2 when TZh51 was incubated on solid mineral salt medium coated with pyrene films. When TZh51 was incubated in liquid mineral salt medium containing 50 and 100 mg/L pyrene, 91.9% and 71.8% pyrene was degraded after 6 days. On the l0th day, maximal vital cells reached 2.0 x 10(8) and 6.0 x 10(8) cfu/mL, respectively. TZh51's ability to degrade pyrene was stronger than strain M11. Moreover, TZh51's vital cells reached 7.2 x 10(8) cfu/g dry soil on the 6th week and 91.4% phenanthrene, 86.9% fluoranthrene and 85.8% pyrene was degraded after 8 weeks, when both TZh51 and plants were used for bioremediation of PAHs-contaminated soil.

Conclusion: TZh51 had strong ability to degrade PAHs. In addition, combined bioremediation of TZh51 and plants was effective for PAHs-contaminated soil bioremediation.