Pathway diversity and stereochemistry of anaerobic degradation of alkyltoluenes/-benzoates

烷基苯广泛存在于原油和各种石油产品中。它们在受污染的含水层或石油储藏层等缺氧自然生境中的生物降解对这些有害有机化合物的环境归宿起着重要作用。在过去的20年中，已经分离并表征了几种能够利用烷基苯作为唯一碳源和能量源的微生物、铁还原菌和硫酸盐还原菌。甲苯是研究芳烃厌氧降解的典型模型化合物。通过将甲苯添加到富马酸酯中，产生作为初始活化产物的苄基琥珀酸酯，引发甲苯的公认厌氧氧化。然后，琥珀酸苄酯转化为苯甲酰辅酶A，这是许多芳香族化合物厌氧催化的中心会聚中间体。苯甲酰基-CoA至二氧化碳的完全氧化经由环还原、开环和β-氧化进行。尽管有相当数量的细菌分离株可以利用这些底物，但对烷基甲苯和相关烷基苯甲酸酯的降解途径知之甚少。在本项目中，我们将研究烷基甲苯/-苯甲酸酯厌氧生物降解的途径多样性和立体化学，特别关注对位异构体。酶促反应和降解途径将通过鉴定相应的代谢产物来支持已鉴定蛋白质的预测功能。

Alkylbenzenes occur widely in crude oil and various petroleum products. Their biodegradation in anoxic natural habitats such as contaminated aquifers or petroleum reservoirs plays an important role with respect to the environmental fate of these hazardous organic compounds. During the last 20 years several denitrifying, iron-reducing and sulfate-reducing bacteria capable of utilising alkylbenzenes as sole source of carbon and energy have been isolated and characterised. Toluene has been the archetypal model compound to study the anaerobic degradation of aromatic hydrocarbons. The well-established anaerobic oxidation of toluene is initiated by its addition to fumarate yielding benzylsuccinate as initial activation product. Benzylsuccinate is then transformed to benzoyl-CoA, the central convergent intermediate in anaerobic catabolism of many aromatic compounds. Complete oxidation of benzoyl-CoA to carbon dioxide proceeds via ring reduction, ring opening and -oxidation. Only little is known about the degradation pathways of alkyltoluenes and related alkylbenzoates, despite a considerable number of bacterial isolates that can utilize these substrates. In this project we will investigate the pathway diversity and stereochemistry of anaerobic biodegradation of alkyltoluenes/-benzoates with a specifc focus on the para-isomers. Enzymatic reactions and degradation pathways will be proposed by underpinning predicted functions of identified protein with the identification of the corresponding metabolites.