| The heavy metal pollution has been a major international environment concern for the whole world. It is not only hazardous to the ecological environment, but also harmful to the human health through the food chain. To some extent, bacteria living in the heavy metal contaminated soils are inclined to become resistant and tolerant to heavy metals. Studying the mechanism of resistance and tolerance can provide theoretical foundation of applying bacterium to remedy heavy metal contaminated soil.Three kinds of bacteria H1, H3, H4 which can tolerate Pb2+ and Cd2+ are separated from the soil polluted by Pb2+ and Cd2+ in zhuzhou city, Hunan Province. These bacteria could survive in solid medium with Pb300Cd200, Pb400Cd300, Pb400Cd300 mg·L-1 respectively. They were preliminarily identified as Sphingobacterium sp., Chryseobacterium sp., Burkholderia sp., respectively, based on the bacterium morphological characters, the basic physiological and biochemical indexes and 16SrDNA sequence homology matching. The removal rates of Pb2+ by three bacteria were no less than 70%, and the removal rates of Cd2+ were over 51%, the accumulation of Pb2+ and Cd2+ in H1 was 93.05 mg·g-1 and 2.65 mg·g-1,respectively.Electron microscope and EDX analysis show that there were particles of Pb and Cd in the strains exterior and interior indicating that the resistance mechanism to Pb, Cd are deposited in internal and external of cellular. The results from Infrared spectra suggest that strains of resistance and tolerance to Pb2+ and Cd2+ were mainly due to the-NH2,-OH,-COOH,-PO43- in cell wall participate in adsorb or combine Pb2+, Cd2+Through analyzing the effect of three bacteria on soil Pb and Cd biological effectiveness and seed germination of Chinese cabbage, we can get the results as follows. When the soils are sterilized, inoculation treatment significantly decreased the contents of exchangeable Pb2+, Cd2+ in the contaminated soil, compared with the non-inoculated control. After inoculating 10 mL microbial agent, the contents of exchangeable Pb2+ reduced by 35.31%,37.98%,24.65% and Cd2+ reduced by 13.39%,18.37%,7.49%, wheras the contents of exchangeable Pb2+ reduced by47.98%,47.97%,49.02% and Cd2+ by 25.39%,29.23%,27.81% when inoculated 20 mL microbial agent. In addition, inoculation treatment promoted seed germination of Chinese cabbage and reduced the uptake of Pb2+ and Cd2+Pot experiment showed that three strains reduced the Pb2+ and Cd2+ contents in shoot and root of Chinese cabbage, furthermore, the effect of sterilization was better than no sterilization. In the Pb300 mg·kg-1 condition, the lead content in roots after accessing strains was lower than control treatment. But in the Pb500 mg·kg-1 condition, the lead content in roots after accessing strains was higher than control treatment. In contaminated soil, three kinds of bacteria can each promote the transformation of Pb2+, Cd2+ to the form of lower bioavailability... |
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