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

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.