L-Ribulose production by an Escherichia coli harboring L-arabinose isomerase from Bacillus licheniformis.

Recombinant Escherichia coli harboring the L: -arabinose isomerase (BLAI) from Bacillus licheniformis was used as a biocatalyst to produce L: -ribulose in the presence of borate. Effects of substrate concentration, the borate to L: -arabinose ratio, pH, and temperature on the conversion of L: -arabinose to L: -ribulose were investigated. L: -Ribulose production was efficient when pH was higher than 9 and temperature was higher than 50 degrees C. Borate addition to the reaction mixture was essential for high conversion of L: -arabinose to L: -ribulose as it resulted in an equilibrium shift in favor of the product. Under the optimal conditions determined by response surface methodology, the E. coli harboring BLAI produced 375 g l(-1) L-ribulose from 500 g l(-1) L: -arabinose at a reaction time of 60 min, corresponding to a conversion yield of 75% and productivity of 375 g l(-1) h(-1). When the resting recombinant E. coli cells were recycled, 85% of the yield was obtained even after seven cycles of reuse. The productivity and final concentration of L: -ribulose obtained in the present study were the highest yet reported.