Enhanced bioconversion of straw cellulose to 2,3-butanediol at low temperature using engineered psychrotrophic bacteria

To enable low-cost 2,3-butanediol (2,3-BD) biorefining, we established an integrated dual-strain, staged coculture that converts straw cellulose to 2,3-BD within a single low-temperature regime. In this study, a cellulose-degrading bacterium Flavobacterium johnsoniae W24H was isolated, which maintains fluidity and antioxidant capacity by adjusting the composition and content of its cell membrane at 15 °C to adapt to low-temperature environments. Simultaneously, it can efficiently degrade cellulose, accumulating 5.87 g/L of reducing sugars within 7 days and exhibiting high cellulase activity. Genomic analysis and molecular docking and enzymatic characterization revealed that W24H possesses a complete cellulase system. Specifically, the key endoglucanase CelB75 and β-glucosidase BglX92 maintain high activity at low temperatures, providing a molecular basis for their low-temperature degradation capability. Under identical low-temperature conditions, the engineered strain W24H- celB75-bglX92 significantly enhanced cellulose saccharification efficiency, achieving a reducing sugar yield of 10.49 g/L. Additionally, by establishing a staged culture system of an efficient cellulose-degrading bacterium (W24H- celB75-bglX92 ) and a 2,3-BD producing bacterium ( Raoultella terrigena HC6), efficient conversion of corn straw cellulose to 2,3-BD was achieved. At 20 °C, compared to the original strain combination, this system optimized the metabolic division of labor between cellulose hydrolysis and product synthesis, resulting in an output of 2,3-BD reaching 0.33 g/g, an increase of 60.1 %. This study achieved efficient biotransformation of straw cellulose into 2,3-BD under low-temperature conditions, providing a foundation for low-energy biorefinery processes with reduced energy input and for the valorization of agricultural waste.