Mechanistic investigations on the pathway of n-alkane oxidation in anaerobic bacteria

烷烃是原油和各种石油产品的主要成分。它们在受污染的含水层或石油储层等缺氧自然环境中的生物降解在全球碳循环中发挥着重要作用。在过去的15年中，已经分离并表征了几种能够利用烷烃作为唯一碳源和能量源的微生物和硫酸盐还原菌。基于代谢产物的鉴定和同位素标记底物的研究，提出了一种在降解细菌菌株HxN 1中完全氧化正己烷为二氧化碳的途径。在初始活化反应中，正烷烃被添加到富马酸酯的双键上，产生琥珀酸（1-甲基戊基）酯（MPS）。MPS通过一系列酶反应进一步转化为支链脂肪酸（4-甲基辛酰基-CoA），然后通过β-氧化降解。该项目的主要目标是获得新的见解，提出的降解途径的重要机制方面，并有助于更好地了解可能的基本差异，在正烷烃与烷基苯氧化的生化机制。特别是，将通过真实标准品的立体选择性合成和分离代谢物的刚性结构归属来确定关键代谢物的立体化学。厌氧烃氧化细菌的底物范围将通过与模型底物和原油的共转化实验来表征。

Alkanes are the main constituents of crude oil and various petroleum products. Their biodegradation in anoxic natural environments such as contaminated aquifers or petroleum reservoirs plays an important role in the global carbon cycle. During the last 15 years several denitrifying and sulphate-reducing bacteria capable of utilizing alkanes as sole source of carbon and energy have been isolated and characterized. Based on the identification of metabolites and studies with isotope labeled substrates a pathway for the complete oxidation of n-hexane to carbon dioxide in the denitrifying bacterium strain HxN1 has been proposed. In the initial activation reaction the n-alkane is added to the double bond of fumarate yielding (1-methylpentyl)succinate (MPS). MPS is further transformed via a sequence of enzyme reactions to a branched fatty acid (4-methyloctanoyl-CoA) which then is degraded by β-oxidation. Main goal of this project will be to obtain new insights into important mechanistic aspects of the proposed degradation pathway, and to contribute to a better understanding of possible fundamental differences in the biochemical mechanisms involved in n-alkane versus alkylbenzene oxidation. In particular, the stereochemistry of key metabolites will be established by stereoselective synthesis of authentic standards and rigid structure assignment of isolated metabolites. The substrate range of anaerobic hydrocarbon oxidizing bacteria will be characterized through co-transformation experiments with model substrates and crude oil.