根瘤菌X9降解西维因的机理研究

西维因的微生物降解一直受到研究人员的关注，但是进展缓慢，直到近三年才取得突破。在假单胞菌C5pp和XWY-1中，它们都通过一个保守的mcb基因簇 (mcbABCDEFGHIJKLMNOPQ)负责西维因的降解。根瘤菌X9是本课题组分离的能以西维因为唯一碳源生长的菌株。鉴于该菌株中的西维因水解酶基因是cehA而不是mcbA，而且根瘤菌降解西维因的全套基因还没有被解析。我们在比较mcb基因簇与菌株X9基因组并结合实验的基础上发现菌株X9的西维因降解途径与假单胞菌C5pp和XWY-1类似，但是在水杨酸到龙胆酸这个步骤有差异，而且负责降解1-萘酚、1,2-二羟基萘和水杨酸的基因不同于mcb基因簇中的相关基因。本项目将以菌株X9为研究对象，克隆和鉴定这些基因，同时研究1-萘酚羟化酶基因的转录调控机制。预期结果将从基因水平上解析菌株X9降解西维因的机理，为西维因污染环境的生物修复提供理论依据。

Carbaryl is one of the representative varieties of carbamate insecticides and it is widely used in the control of agricultural and forestry pests. However, the environmental and ecological problems brought about by its residues have also attracted people's attention. The microbial degradation of carbaryl has been the focus of researchers, but progress has been slow until a breakthrough in the last three years. In Pseudomonas sp. strain C5pp and Pseudomonas sp. XWY-1, they both harbor a conserved mcb gene cluster (mcbABCDEFGHIJKLMNOPQ), which is responsible for the degradation of carbaryl. Rhizobium sp. X9 is a strain isolated by our group that can use carbaryl as the sole carbon source for growth. As the carbaryl hydrolase gene in stain X9 is cehA instead of mcbA, and the whole genes responsible for the complete degradation pathway of carbaryl in Rhizobium have not been elucidated. On the basis of comparing the mcb gene cluster with the genome sequence of strain X9 and the results of some experiments, we find that the carbaryl degradation pathway in strain X9 is similar to those in strains C5pp and XWY-1, but the difference lies in the step of salicylic acid to gentisic acid, and also the genes responsible for the degradation of 1-Naphthol, 1,2-Dihydroxynaphthalene and salicylic acid are different from those in the mcb gene cluster. The target of this project is to clone and identify these genes, and also investigate the transcriptional regulation mechanism of the 1-Naphthol hydroxylase gene. The expected results of this project will elucidate the degradation mechanism of carbaryl in strain X9 from the genetic level, and provide a theoretical basis for the bioremediation of carbaryl-contaminated environments.