Direct and highly productive conversion of cyanobacteria to ethanol with CaCl addition.

BACKGROUND

The cyanobacterium shows promise as a carbohydrate feedstock for biofuel production. The glycogen accumulated in can be extracted by lysozyme-degrading the peptidoglycan layer of the bacterial cell walls. The extracted glycogen can be converted to ethanol through hydrolysis by amylolytic enzymes and fermentation by the yeast . Thus, in the presence of lysozyme, a recombinant yeast expressing α-amylase and glucoamylase can convert directly to ethanol, which would simplify the procedure for ethanol production. However, the ethanol titer and productivity in this process are lower than in ethanol production from cyanobacteria and green algae in previous reports.

RESULTS

To increase the ethanol titer, a high concentration of biomass was employed as the carbon source for the ethanol production using a recombinant amylase-expressing yeast. The addition of lysozyme to the fermentation medium increased the ethanol titer, but not the ethanol productivity. The addition of CaCl increased both the ethanol titer and productivity by causing the delamination of polysaccharide layer on the cell surface of . In the presence of lysozyme and CaCl, ethanol titer, yield, and productivity improved to 48 g L, 93% of theoretical yield, and 1.0 g L h from , corresponding to 90 g L of glycogen.

CONCLUSIONS

We developed an ethanol conversion process using a recombinant amylase-expressing yeast from with a high titer, yield, and productivity by adding both lysozyme and CaCl. The direct and highly productive conversion process from via yeast fermentation could be applied to multiple industrial bulk chemicals.