Papermaking wastewater treatment coupled to 2,3-butanediol production by engineered psychrotrophic Raoultella terrigena

The simultaneous bioremediation and bioconversion of papermaking wastewater by psychrotrophic microorganisms holds great promise for developing sustainable environments and economies in cold regions. Here, the psychrotrophic bacterium Raoultella terrigena HC6 presented high endoglucanase (26.3 U/mL), xylosidase (732 U/mL), and laccase (8.07 U/mL) activities for lignocellulose deconstruction at 15 degrees C. mRNA monitoring and phenotypic variation analyses confirmed that cold-inducible cold shock protein A (CspA) facilitated the expression of the cel208, xynB68, and lac432 genes to increase the enzyme activities in strain HC6. Furthermore, the cspA gene-overexpressing mutant (strain HC6-cspA) was deployed in actual papermaking wastewater and achieved 44.3%, 34.1%, 18.4%, 80.2% and 100% removal rates for cellulose, hemicellulose, lignin, COD, and NO3- -N at 15 degrees C. Simultaneously, 2,3-butanediol (2,3-BD) was produced from the effluent with a titer of 2.98 g/L and productivity of 0.154 g/L/h. This study reveals an association between the cold regulon and lignocellulolytic enzymes and provides a promising candidate for simultaneous papermaking wastewater treatment and 2,3-BD production.

Automated summary

This study demonstrates the potential of psychrotrophic microorganisms, particularly Raoultella terrigena HC6, for simultaneous bioremediation and bioconversion of papermaking wastewater in cold regions. The HC6 strain exhibited high enzymatic activities for lignocellulose deconstruction at 15 degrees C, facilitated by the cold-inducible cold shock protein A (CspA). The mutant strain HC6-cspA overexpressing the cspA gene showed great performance in removing cellulose, hemicellulose, lignin, COD, and NO3- -N, while also producing 2,3-butanediol as a valuable byproduct.