Sunday, April 29, 2007

Tailoring a thermophilic bacterium for optimal bioethanol production from lignocellulosic biomass

Marie J. Mikkelsen, BioGasol ApS, Soltofts plads, bygn 227 / rum 040, DK-2800 Lyngby, Denmark and Birgitte K. Ahring, Bsel, WSU, 2710 University Drive, Richland, WA 99354, Denmark.

A large number of thermophilic bacteria were isolated and screened for their potential as ethanol producers in high concentrations of lignocellulosic hydrolysate. The test included tolerance towards ethanol and inhibitors. Of these many isolates, Thermoanaerobacter BG1 was chosen for its ability to grow on non-detoxified pre-treated lignocellulosic materials at 70°C. It has a natural high ethanol yield and is able to grow on a large array of hexose and pentose sugars including glucose, galactose, mannose, xylose and arabinose as well as the polymers starch and xylan. Here we report on several genetic modifications of BG1 including gene deletions, insertions of heterologous genes, and expression level manipulation. One of the resulting strains was able to produce ethanol with yields of up to 0.47 g/g sugar. Fermentation of pentoses in wet-oxidised, enzymatically treated and yeast fermented wheat straw is currently tested in an 800 l continuous reactor using one of the mutant strains. The results from this test will further be discussed.