Urease expression in a Thermoanaerobacterium saccharolyticum ethanologen allows high titer ethanol production

Genes encoding the enzyme urease were integrated in a Thermoanaerobacterium saccharolyticum ethanologen. The engineered strain hydrolyzed urea, as evidenced by increased cellular growth and elevated final pH in urea minimal medium and urease activity in cell free extracts. Interestingly, replacement of ammonium salts with urea resulted in production of 54 g/L ethanol, one of the highest titers reported for Thermoanaerobacterium. The observed increase in ethanol titer may result from reduced pH, salt, and osmolality stresses during fermentation. Urea utilization is attractive for industrial scale fermentation, where pH control is technically challenging and increased ethanol titer is desirable.