一株含双降解质粒的红球菌（Rhodococcus sp.）二噁英降解机理研究

二噁英在我国有广泛的污染源与污染分布区域。有氧条件下细菌的降解作用是去除二噁英污染的重要途径，由双加氧酶催化的起始双羟化是二噁英降解的关键步骤。DfdA与DbfA分别为在不同革兰氏阳性降解菌中发现的催化起始双羟化的双加氧酶，在极少数革兰氏阳性降解菌中同时含有两种酶。本项目拟以一株含有DfdA与DbfA，且酶的编码基因分别位于不同降解质粒（pDF01与pDF02）的红球菌Rhodococcus sp. strain p52为研究对象，研究其二噁英降解机理。通过分析DfdA与DbfA底物范围的差异、降解协同性以及酶基因转录活性的差异，揭示两种双加氧酶在二噁英降解中的协作；在此基础上，进一步分析降解质粒pDF01与pDF02在二噁英降解、质粒接合迁移与稳定遗传中的协作。通过本项目的研究可为开发、利用、改造微生物更有效去除二噁英等污染物提供理论依据。

Dioxin pollution is one of the severe problems in China. Biodegradation by aerobic bacteria is an important way to remove dioxins. The crucial step in degradation of dioxins is the initial dihydroxylation catalyzed by dioxygenases which are encoded by conservative dfdA or dbfA in distinct Gram positive degraders. However, a few strains harbor both dfdA and dbfA, which may expand the substrate range and improve removal activity. It is unclear that how the dioxygenase DfdA and DbfA cooperate in such strain during degradation of dioxin. Genes involved in initial ring-cleavage of dioxin are usually harbored by catabolic plasmid. It can be expected that cooperation of the catabolic plasmids in the strain favors its catabolic ability and environmental adaptation. Cooperation of the catabolic plasmids, especially the dioxin catabolic plasmids, remains to be explored. The proposed research involves the cooperation of the dioxygenase DfdA and DbfA in a dioxin-degrader Rhodococcus sp., as well as that of two dioxin catabolic plasmids which harbor dfdA and dbfA, respectively. To learn the cooperation of DfdA and DbfA, the substrate ranges of the enzymes, the synergy effects during degradation, and the transcriptional activities of dfdA and dbfA will be investigated. Based on the understanding of collaborative dioxygenases, cooperation of dioxin catabolic plasmids (pDF0 and pDF02) during degradation of dioxins as well as conjugative transfer and stable maintaining of plasmids will be elucidated. The proposed study will provide insight into dioxin biodegradation with Gram positive bacteria, and therefore contribute to the bioremediation of dioxin.