Simultaneous and selective production of exopolymers and polyols by metabolically engineered Bacillus licheniformis strains

Abstract

Bacillus licheniformis has tremendous potential for the production of exopolymers that include polyglutamic acid (PGA), levan and exopolysaccharide (EPS); and polyols among which are glycerol and 2,3-butanediol (BDO) isomers. For simultaneous and selective production of exopolymers and polyols, cultivation/fermentation, metabolic engineering, and separation technologies were combined and evaluated in this study. Specific exopolymers could be produced by changing carbon source and temperature, and through biofilm-associated gene (epsAB and pgsBCAE) manipulation. The specific production of polyols was achieved by the deletion of appropriate genes (dgp, budC, and gdh). The most efficiently and selectively produced exopolymer and polyol were levan and (2 R,3 S)-BDO. Fed-batch fermentation confirmed that 71.0 g/L of levan with 99% selectivity of exopolymer and 88.6 g/L of (2 R,3 S)-BDO with 100% selectivity of polyol could be obtained in 72 h. Simultaneous and selective production of various combinations of exopolymers and polyols appears to be feasible for efficient production of bio-based products.