Direct microbial production of 2,3-Butanediol from inulin by Bacillus velezensis R22 through the synergistic action of membrane and cytoplasmic inulinases

Abstract

The present study investigates the natural ability of Bacillus velezensis R22 to produce 2,3-BD from two inulin-rich substrates – insoluble and soluble chicory flour. After complex optimization of the media content and process parameters by consecutive application of Plackett-Burman design and response surface methodology, the strain R22 was capable of producing 71.2 g/L (95.5 % R,R-2,3-BD) and 96.4 g/L 2,3-BD (86.2 % R,R-2,3-BD) from insoluble and soluble chicory flour without preliminary hydrolysis. The optimal conditions were: K₂HPO₄ concentration of 3.43 g/L, pH 6.68, and agitation speed of 363 rpm. The total inulinase activity of R22 ranged between 85 and 94 U/mL and was provided by the synergistic action of two enzymes: cytoplasmic SacC and membrane-located LevB, which were purified and characterized. The ability to directly convert inulin, its non-pathogenic nature, and the formation of predominantly R,R-2,3-BD singled out B. velezensis R22 as a new promising industrial producer of 2,3-BD from inulin-rich plant biomass.