Temperature-dependent acetoin production by Pyrococcus furiosus is catalyzed by a biosynthetic acetolactate synthase and its deletion improves ethanol production

Diep M.N. Nguyen, Gina L. Lipscomb, Gerrit J. Schut, Brian J. Vaccaro, Mirko Basen, Robert M. Kelly, Michael W.W. Adams

Department of Biochemistry and Molecular Biology, University of Georgia, Athens, GA 30602, USA.

Abstract

The hyperthermophilic archaeon, Pyrococcus furiosus, grows optimally near 100°C by fermenting sugars to acetate, carbon dioxide and molecular hydrogen as the major end products. The organism has recently been exploited to produce biofuels using a temperature-dependent metabolic switch using genes from microorganisms that grow near 70°C. However, little is known about its metabolism at the lower temperatures. We show here that P. furiosus produces acetoin (3-hydroxybutanone) as a major product at temperatures below 80°C. A novel type of acetolactate synthase (ALS), which is involved in branched-chain amino acid biosynthesis, is responsible and deletion of the als gene abolishes acetoin production. Accordingly, deletion of als in a strain of P. furiosus containing a novel pathway for ethanol production significantly improved the yield of ethanol. These results also demonstrate that P. furiosus is a potential platform for the biological production of acetoin at temperatures in the 70–80 °C range.

Keywords: Archaea; Hyperthermophile; Genetic engineering; Acetolactate synthase; Acetoin; Ethanol.