Cleaner 2,3-butanediol production from unpretreated lignocellulosic biomass by a newly isolated Klebsiella pneumoniae PX14

Bioconversion lignocellulosic biomass (LCB) to 2,3-butanediol (2,3-BDO) is a sustainable and energy-intensive practice, but its economic feasibility has been hindered by costly pretreatment and the cumbersome fermentation process. Herein, a lignocellulolytic strain Klebsiella pneumoniae PX14 is isolated from insect gut, showing effective degradation on unpretreated LCB with rates of 51.48 % for cellulose, 62.13 % for hemicellulose, and 41.42 % for lignin, while with a low 2,3-BDO titer of 3.26 g/L. Consequently, the secretory proteins of PX14 cultured on the bamboo biomass-containing medium are extracted for the construction of an enzyme cocktail with commercial cellulase. The designed enzyme cocktail achieves efficient saccharification of the unpretreated LCB, resulting in 42.90 g/L reducing sugars released, which is significantly higher than that from the secretory protein or cellulase only. These high sugars titer is also effective conversion to 2,3-BDO of 19.11 g/L titer by PX14 after further optimization. For the first time, the enzyme cocktail is tried for application in simultaneous saccharification and fermentation (SSF) of 2,3-BDO from unpretreated LCB. This fed-batch SSF resulted in 47.46 g/L of 2,3-BDO with 0.36 g/L/h productivity under high solid loading of 20 % due to the high substrate concentration tolerance of PX14. Finally, whole-genome sequencing reveals the robustness of K. pneumoniae PX14 and its molecular mechanism for such a process. These results provide a robustness strain of K. pneumoniae PX14 and its novel application in SSF of 2,3-BDO from unpretreated LCB, showing a great breakthrough in this process.