| Cadmium is a kind of heavy metal element which has strong toxicity to animals and plants, Meanwhile, Cadmium also can be easily absorbed by crops from the soil characteristics of the environment. While crops being eaten as food the Cadmium would endanger human's health. With the development of biological science and technology, The research of heavy metal cadmium in the environment of microbial degradation is increasing and deepening. A certain number of microorganisms was discovered with ability to adsorb heavy metal ion, which has strong application prospects in the remediation of heavy metal cadmium pollution. In this paper, We selected a solid plate screening method to screen the strains with strong ability of cadmium resistance, comparing and studying the characters of the low cadmium resistant strains, the results are as follows:1. In this study, the soil samples were collected from the surrounding soil of the waste landfill site in Zhuzhou chemical smelter, Through cadmium gradient experiments, The writer screened out 18 medium normal growth of Trichoderma strains in a concentration of cadmium ions on PDA 50mg/L, then increase the cadmium concentration gradually to rescreen strong Cadmium Tolerance normal growth of Trichoderma strain T61 with capable of cadmium ion concentration under 400mg/L, and the normal growth of the weak cadmium resistant Trichoderma strain T21 with the weakest cadmium tolerance only in the cadmium ion concentration under 50mg/L.2. Through the morphological observation of T61 and T21 strains, T61 strains were found with a large amount of white mycelium spread over conidia on PDA medium, Mycelium like white curls, Conidia are sub-spherical and ovoid or short ellipsoidal, These morphological description corresponded to the description of Trichoderma harzianum.T21 strains were found with white curly-shaped mycelium on PDA medium, Some mycelium are gray.Conidia are sub-spherical, The spore wall is smooth and translucent, These morphological description corresponded to the description of Trichoderma hamatum, Through the analysis of 28S rDNA sequence of T61 and T21 strains, The results show that similarity between T61 and T.harzianum is 96%, Combined with T61 morphological observation,T61 was identified as Trichoderma harziarum strain; The results show that similarity between T21 and T. hamatum is 95%, Combined with T21 morphological observation,T61 was identified as Trichoderma hamatum strain3. According to the determination of the degradation rate of cadmium ions in T61, T21 and 2-14hours by AAS, the writer found that in the 6 hour, the degradation rate of cadmium of T61, T21 strain are respectively 43% and 31%, which accounted 96% and 84% of the total degradation rate. It indicated that the degradation of cadmium ions of T21 and T61 was carried out in a short time (6hours). Afterwards, the result of single variable temperature and pH degradation of cadmium ion experiments on T61, T21 showed that optimal temperatures of T61, T21 strains cadmium degradation are 28 ?; pH 4. When the pH is 4, temperature of 28?, effect of T61, T21 strain cadmium degradation reaches the maximum values 58% and 42%.4. By comparing the T61 and T21 strains mycelium through electron microscope,the writer found that the mycelium of T61 strain is more stout, the surface is more smooth and flat than the T21 strain. Under cadmium stress, T21 strain appeared obviously irregular expansion, mycelium became thin, water loss and deformation; while T61 strains in cadmium ion stress conditions, hyphae also appeared a certain degree of thinning, but smaller degree than the T21, and there is no large irregular expansion, the mycelium on the surface is quite smooth. |
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