Thermophilic Bacillus coagulans Requires Less Cellulases for Simultaneous Saccharification and Fermentation of Cellulose to Products than Mesophilic Microbial Biocatalysts

Abstract

Ethanol production from lignocellulosic biomass depends on simultaneous saccharification of cellulose to glucose by fungal cellulases and fermentation of glucose to ethanol by microbial biocatalysts (SSF). The cost of cellulase enzymes represents a significant challenge for the commercial conversion of lignocellulosic biomass into renewable chemicals such as ethanol and monomers for plastics. The cellulase concentration for optimum SSF of crystalline cellulose with fungal enzymes and a moderate thermophile, Bacillus coagulans, was determined to be about 7.5 FPU g(-1) cellulose. This is about three times lower than the amount of cellulase required for SSF with Saccharomyces cerevisiae, Zymomonas mobilis, or Lactococcus lactis subsp. lactis whose growth and fermentation temperature optimum is significantly lower than that of the fungal cellulase activity. In addition, B. coagulans also converted about 80% of the theoretical yield of products from 40 g/L of crystalline cellulose in about 48 h of SSF with 10 FPU g(-1) cellulose while yeast, during the same period, only produced about 50% of the highest yield produced at end of 7 days of SSF. These results show that a match in the temperature optima for cellulase activity and fermentation is essential for decreasing the cost of cellulase in cellulosic ethanol production.

Evolution of D-lactate dehydrogenase activity from glycerol dehydrogenase and its utility for D-lactate production from lignocellulose

“…S6) With this enzyme loading, the productivity of a typical lactic acid bacterium Lactococcus lactis at 40°C was only 1∕3 that of strain QZ19. These results are in agreement with previous studies on lower cellulase requirements for optimal L-lactate production by unmodified B. coagulans compared to other lactic acid bacteria (21). Strain QZ19 is better suited for SSF of cellulose to D-lactate and requires significantly lower level of cellulase for cost-effective metabolism of this nonfood carbohydrate.…”

“…Growth and fermentation conditions have been described previously (15,(21)(22)(23). Cultures were grown in L-broth (LB) at pH 5.0 or 7.0, as needed.…”

“…This bacterium ferments both hexoses and pentoses to L(+)-lactic acid using the highly efficient pentose-phosphate pathway ( Fig. 1) at 50-55°C and pH 5.0, conditions that are optimal for commercial fungal cellulases (15,17,21). Native strains produce optically pure L(+)-lactic acid at concentrations as high as 180 g L −1 in fed-batch fermentations from either glucose or xylose, and perform well during simultaneous saccharification and fermentation (SSF) of cellulose using fungal cellulases (21,22).…”

“…1) at 50-55°C and pH 5.0, conditions that are optimal for commercial fungal cellulases (15,17,21). Native strains produce optically pure L(+)-lactic acid at concentrations as high as 180 g L −1 in fed-batch fermentations from either glucose or xylose, and perform well during simultaneous saccharification and fermentation (SSF) of cellulose using fungal cellulases (21,22). This match in optima both for the fermentation of B. coagulans and for fungal cellulase activity allowed a fourfold reduction in cellulase usage in comparison to SSF with mesophilic bacterial biocatalysts (21).…”

“…Native strains produce optically pure L(+)-lactic acid at concentrations as high as 180 g L −1 in fed-batch fermentations from either glucose or xylose, and perform well during simultaneous saccharification and fermentation (SSF) of cellulose using fungal cellulases (21,22). This match in optima both for the fermentation of B. coagulans and for fungal cellulase activity allowed a fourfold reduction in cellulase usage in comparison to SSF with mesophilic bacterial biocatalysts (21). B. coagulans also grows and ferments sugars in mineral salts medium with inexpensive corn steep liquor (0.25%, wt∕vol) supplementation in contrast to lactic acid bacteria that require complex nutrients (8,15,18).…”