Regulation of clostridial solvent production by Quorum sensing

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Anaerobic bacteria of the genus Clostridium are well known for their ability to convert diverse feedstocks into industrially important solvents. In the past, clostridial fermentations were used for the large scale production of acetone and butanol; nowadays ethanol-forming species are also being exploited which can grow on industrial waste gases. Low solvent yields/titres remain a concern and, thus, considerable efforts have been devoted to improving the organisms' performance through metabolic engineering. However, decisive breakthroughs are yet to be made. A major reason for this is our limited understanding of the organisms' physiology and metabolism, in particular the mechanisms that govern timing and extent of solvent formation. In previous DTP projects, we discovered a large number of quorum sensing systems in solvent-producing clostridia, which enable individual cells of a population to communicate with one another via diffusible signal molecules. We have shown that many of these systems strongly influence the production of acetone, butanol and ethanol, but the underlying molecular mechanisms remain unknown. However, a thorough understanding of the physiological factors and regulatory mechanisms constraining solvent formation is a prerequisite for successful metabolic engineering of the respective species. Using an established industrial strain, the specific aims of this study are to (i) establish the transcriptional, translational, and physiological changes occurring in quorum sensing-deficient mutants (ii) identify the genes directly regulated by specific quorum sensing regulators (iii) exploit this knowledge for the generation of strains in which solvent formation can be maximised by earlier or higher expression of the genes involved