(R,R)-2,3-Butanediol bioproduction using unsterile-untreated sugarcane molasses and its influence on rice cultivation in the field

2,3-Butanediol (2,3-BDO) is a C4 platform bio-based chemical with wide applications in industry and agriculture. However, its large-scale deployment is constrained by high production cost, and its utilization in field-grown rice has not been reported to date. In this study, cost-effective microbial production of ( R , R )-2,3-BDO by Bacillus subtilis was achieved using a simple fermentation medium composed of unsterilized, untreated sugarcane molasses and corn steep liquor powder, and its influence on rice cultivation was subsequently investigated. Following optimization of the fermentation medium and agitation speed, a combined titer of 52.2 g/L of 2,3-BDO and acetoin was obtained in a 72-h batch fermentation (0.2 vvm, 275 rpm), in which the ( R , R )-2,3-BDO concentration reached 42.7 g/L, accounting for 93.5% of the total 2,3-BDO. Pot trials were conducted to identify the optimal 2,3-BDO concentration for promoting rice seedling development, and 0.1 mmol/L was determined to be the most effective. Significant agronomic benefits were observed in subsequent field test: the shoot and root dry weights of rice seedlings were increased by 54% and 31%, respectively, while the chlorophyll content was maintained at 30–40% higher than the control throughout the growing season. Furthermore, the panicle number per hill and grain yield were increased by 16% and 32%, respectively, and the rice composition was kept constant. To our knowledge, this is the first study demonstrating that exogenous 2,3-BDO could promote rice seedling growth and stimulate tillering, ultimately resulting in improved rice yield.