Monday, May 5, 2008
7-38

Thermophilic Bacillus coagulans as an Effective Microbial Biocatalyst for SSF of Cellulose to Products

Mark S. Ou, N. Mohammed, Lonnie O. Ingram, and K. T. Shanmugam. Department of Microbiology and Cell Science, University of Florida, P.O. Box 110700, Building 981, Museum Rd, Gainesville, FL 32611

Bioconversion of cellulose to fuels and chemicals requires hydrolysis of cellulose by fungal cellulases and fermentation of the resultant sugars by microbial biocatalysts. Simultaneous saccharification and fermentation (SSF) overcomes product inhibition of cellulase activity. However, the optimum growth temperature of industrial microbial biocatalysts (yeast and lactic acid bacteria) dictates the SSF temperature as 30-35ºC that is not optimal for fungal cellulase activity (50ºC). This lower SSF temperature increases the amount of cellulases needed for optimum SSF of cellulose with associated increase in product cost. Towards reducing the cost of cellulases needed for SSF of cellulose to products, we are developing Bacillus coagulans as microbial biocatalyst that grows at 50-55ºC matching the fungal enzyme activity optimum. SSF of cellulose with B. coagulans strain 36D1 was compared with that of Saccharomyces cerevisiae, Zymomonas mobilis and Lactococcus lactis, microbial biocatalysts used by ethanol and lactic acid industries. SSF of cellulose with fungal cellulases was conducted with pH control at conditions that are optimal for each organism. Based on volumetric productivity, SSF of cellulose at 50-55ºC with B. coagulans required about 4-times less cellulases in comparison to SSF at 35ºC with the other three organisms. B. coagulans as the microbial biocatalyst in SSF of cellulose at 55ºC can significantly reduce the cost of fungal cellulases in optically pure L(+)-lactic acid production. Engineering of B. coagulans or other thermophilic bacteria for ethanol production can reduce the cost of cellulosic ethanol simply by matching the microbial biocatalyst to the optimum for fungal cellulase activity.

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