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

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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.