4-羟基苯甲酸（4HBA）本来是在自然界中存在的芳香族化合物，但随着含有4HBA的工业产品的大量使用和排放，4HBA已成为常见的有机污染物。微生物降解4HBA的途径有原儿茶酸开环途径，邻苯二酚开环途径和厌氧微生物的苯环开环途径。Bacillus sp. B1菌株是从堆肥中分离出来的嗜热性细菌，拥有各种各样的芳香族化合物降解途径。B1菌株降解4HBA的途径不同于其他常见微生物，是通过龙胆酸开环途径。从4HBA转化为龙胆酸的过程包括一个叫做“NIH重排”的反应。我们在前期工作中预测出有辅酶A连接酶、单加氧酶和裂解酶的参与，但是其反应机制尚不明了。本项目的研究内容是：（1）编码NIH重排反应相关酶的基因研究；（2）各个酶促反应的热动力学特性研究。通过这些研究彻底阐明从4HBA转化为龙胆酸过程中的NIH重排反应全貌，并揭示在自然界中发挥的作用。

4-Hydroxybenzoate (4HBA) is a naturally occurring aromatic compound, but with the extensive use and emissions of 4HBA containing industrial products, it becomes one class of major common organic pollutants. There are three 4HBA catabolic pathways: protocacechuate cleavage pathway, catechol cleavage pathway and anaerobic degradation pathway in anaerobes. Bacillus sp. B1, a thermophilic bacterium, originally isolated from compost, has a lot of catabolic pathways for aromatic compound degradation. The 4HBA catabolic pathway in strain B1 is different from other microorganisms, the benzene ring fisson is through gentisate. The conversion of 4HBA to gentisate includes a reaction called “NIH shift”. Our preliminary study has suggested that CoA ligase, monooxygenase and lyase may be involved in this reaction, but underlying mechanism is still unknown. In this proposed work, we will study on: (1) genes encoding enzymes involved in NIH shift; (2) thermodynamic properties of each enzymatic reaction.Based on these results, we can elucidate a complete mechanism for NIH shift involved in degradation of 4HBA to gentisate, and unveil a role of NIH shift related genes in the global carbon cycle.