Sunday, May 3, 2009
2-32
Regulation of pfl in B. coagulans
Mun Su Rhee, L.O. Ingram, and K.T. Shanmugam. Department of Microbiology and Cell Science, University of Florida, Bldg 981 Museum RD, Gainesville, FL 32611
The sporogenic lactic acid bacterium, Bacillus coagulans, grows and ferments sugars such as glucose and xylose at 50-55 °C and pH 5.0, the optimum temperature and pH for the activity of commercial fungal cellulases. Because of these properties, simultaneous saccharification and fermentation (SSF) of cellulose to products by B. coagulans requires less cellulase for optimum volumetric productivity than at a sub-optimal temperature for SSF utilizing yeast. During growth in pH-controlled fermentations of glucose at 50°C and pH 5.0, B. coagulans strain 36D1 produced lactate as the fermentation product. Although the genes encoding pyruvate formate-lyase (PFL) are present in the genome of B. coagulans strain 36D1, formate, the distinctive product of PFL activity, was not detected in the broth of the pH 5.0 culture either during the growth phase or early stationary phase. However, growth of B. coagulans at a medium pH of 7.0 supported PFL activity as evidenced by accumulation of formate during the late-log phase of growth. In agreement with this observation, the pfl mRNA was about 3-times higher in cells grown at pH 7.0 compared to cells grown at pH 5.0. The pfl mRNA was detected only in anaerobically grown cells and not in cells grown with aeration. These results suggest that the transcription of pfl in Bacillus coagulans is controlled by the level of oxygen, culture pH and growth stage.