Anaerobic alkane and alkene metabolism in sulfate-reducing prokaryotes

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The best studied alkane- and alkene-degrading species of sulfate-reducing bacteria are Candidatus “Desulfococcus oleovorans” and Desulfatibacillum alkenivorans, for which complete genome sequences are available. In addition, Archaeoglobus fulgidus was recently described as anaerobic alkane- and alkene-degrading archaeon. For 1-alkenes, an initial hydration to alcohols with subsequent oxidation to fatty acids has been proposed as initial reaction. However, the type of enzyme hydratising alkenes to alcohols is unknown. While anaerobic alkane degradation is initiated in many organisms by addition of the subterminal methylene group to fumarate, the genome of “D. oleovorans” does not contain any of the corresponding genes. It is remarkable that the genomes of “D. oleovorans” und A. fulgidus instead code for an ethylbenzene dehydrogenase-like molybdenum enzyme, although the organisms does not degrade ethylbenzene. These genes are lacking in the genome of D. alkenivorans, which degrades alkanes via fumarate addition. Finally, all three genomes contain genes for molybdo- or tungsto-enzymes similar to acetylene hydrates, the only currently known enzyme adding water to a multiple bond. We intend in this project to identify the enzymes initiating the anaerobic degradation of alkanes and alkenes by proteomic approaches and characterise the native or recombinant proteins by biochemical methods. In addition, we want to characterise the paralogs of ethylbenzene dehydrogenase and acetylene hydratase from “D. oleovorans” or A. fulgidus, independently of their actual contributions to the metabolic pathway of alkanes or alkenes.