This is the first revelation of how a bacterium chooses from its more than 100 enzymes to break down a particular biomass. Once we know how a bacterium targets a particular type of biomass, we should be able to boost that process to draw ethanol from biomass far more efficiently that we can today.

—Prof. David H. Wu, University of Rochester

The team investigated Clostridium thermocellum—an anaerobic, thermophilic, cellulolytic, and ethanogenic bacterium. C. thermocellum has that ability to turn biomass into ethanol in one step, but is not used at the industrial scale yet because the process of breaking down the plant’s cellulose is much too inefficient.

The key, Wu surmised, was to find out what enzymes the bacterium uses to accomplish its feat, and then boost its ability to produce those enzymes. The bacterium uses more than 100 enzymes, and any of the millions of combinations of them may be the combination to break down a particular biomass.

C. thermocellum produces low levels of many of its enzymes at any one time. When the bacterium comes in contact with wood, for instance, a few of its enzymes break down some of that wood. A product of that tiny reaction is a sugar called laminaribiose that diffuses into the cell. There it deactivates a repressor for two genes, which wake up and start pumping out the two triggers the full production of wood-degrading enzymes CelC and LicA.

Wu’s paper shows the first time the triggering pathway for enzyme production in this bacterium has been revealed, and it was only possible because the C. thermocellum genome was just recently sequenced (on project on which Wu collaborated with the US Department of Energy).

Wu is now working to re-engineer C. thermocellum to express an abundance of particular genes so it can readily and efficiently produce ethanol from a particular biomass. He’s also continuing the genome-wide search for enzyme combinations that will degrade and ferment grasses, corn stovers, and even food waste.

I don’t think this is the revolution that makes ethanol a mainstay, but I believe this is a part of what will lead to the revolution.

—David Wu

Resources:

• “Induction of the celC operon of Clostridium thermocellum by laminaribiose”; Michael Newcomb, Chun-Yu Chen, and J. H. David Wu; Proc. Natl. Acad. Sci. USA, 10.1073/pnas.0700087104