| Hexachlorocyclohexanes (HCHs), as a typical organochlorine pesticide, has been widely used in agricultural production in China. Although HCHs have been banned for agricultural applications since 1983 in China due to the perniciousness, the residues of HCHs were still detected in Chinese agricultural soils because of the persistence of this pesticide. Hexachlorocyclohexane is known as endocrine disruptors and carcinogens, which is a hazard to health. Therefore, people have try to find the HCHs degrading bacterium and predict the residual dynamics of HCHs in order to restore the polluted environment by microorganism.At present, the Sphingobium japonicum UT26 and Sphingomonas paucimobilis B90 are the HCHs degrading bacterium which were studied by many people. The most well studied pathway for degradation of HCHs was found in Sphingobium japonicum UT26 through the study of this bacteria. In the biodegradation process, HCHs are mediated by lin genes and converted to ?-ketoadipate through upper and lower pathways. With the influence of linGH and linJ genes, ?-ketoadipate is further converted to succinyl-CoA and acetyl-CoA, respectively. Then, both of them enter into the tricarboxylic acid (TCA) cycle. In the process, Sphingomonads make this synthetic compound return to the material cycle in nature by a harmlessly way. Although there are many HCHs-degrading bacteria, the researchs still focus on the degradation relationship while the distribution characteristics between the HCHs-degrading bacteria and HCHs is still little known to us.Therefore, in this study, soil samples were collected from various croplands in 28 places in China, we try to explore the PCR primers and reaction conditions of HnA gene, find the optimal PCR method to amplify the UnA gene from soil DNA, investigate the residues of HCHs in Chinese agricultural soils, examine the diversity and abundance of Sphingomonads through the high throughput sequencing and qPCR, analyse the relationship of spatial distribution between the Sphingomonads and HCHs.After the analysed of the HCHs residues and 16S rRNA gene sequences in Chinese agricultural soils, the experimental results are as follows:Total HCHs had a mean level of 2.30 ng/g and its concentrations ranged from 0.42 to 9.69 ng/g in Chinese agricultural soils. In the four chief HCHs isomers (?-HCH,?-HCH, ?-HCH and 8-HCH), the concentrations of ?-HCH is highest and the residues of a-HCH and y-HCH are relatively low. The EF values of chiral a-HCH possessed a great variation, ranging from 0.10 to 0.84 in various agricultural soils. In addition, The analysis of 16S rRNA gene sequences suggested that this kind of bacteria sequences could be classified as four known genera in 28 samples, including "Sphingomonas," "Novosphingobium" "Sphingopyxis," "Sphingobium". "Sphingomonad Sphingomonas", a most broadly distributed genus, which is the dominant genera among the four genera and detected in all samples. Pearson correlation analyses indicated that the diversity of the Sphingomonads bacteria was significantly related to the concentrations of ?-HCH (R=-0.390, P<0.05).The result of qPCR assay of linA gene suggested that there is a difference in the abundance of Sphingomonads in various samples. The abundance of Sphingomonads are relatively low in some samples. The difference of the abundance of Sphingomonads suggested that the potential of HCHs biodegradation is different in various samples. Pearson correlation analyses suggested that there is no significantly correlated between the abundance of Sphingomonads and HCHs residues, While the abundance of Sphingomonad bacteria was significantly related to the concentration of y-HCH (R=-0.425,P<0.05). The correlations between the Sphingomonads and HCH isomers could be used to explain the distribution characteristics of some HCHs isomers and predict the residual dynamics of HCHs. |
PDF Full Text Request