Abstract
Background: Integrated management of hemicellulosic fraction and its economical transformation to value-added products is the key driver towards sustainable second-generation biorefineries. In this aspect microbial cell factories are harnessed for sustainable production of biochemicals by valorising C5 and C6 sugars generated from agro-industrial waste. However, most of the strains can effectively consume C6 sugars but lacks pentose metabolism pathway. The effective utilization of both pentose and hexose sugars is key for economical biorefinery. Results: In the current study, the ability of a newly isolated xylose assimilating Pichia fermentans was explored for xylitol production. The wild type strain robustly grew on xylose and produced xylitol with >40% conversion yield. Mutagenesis with ethyl methanesulphonate (EMS) yielded seven mutants. The mutant obtained after 15 min exposure, exhibited best xylose bioconversion efficiency. This mutant under shake flask conditions produced maximum xylitol titre and yield of 34.0 g/L and 0.68 g/g, respectively. oweverHoHHHoHowever, under same conditions, the control wild type strain accumulated 27.0 g/L xylitol with a conversion yield of 0.45 g/g. Improved performance of the mutant was attributed to 34.6% activity enhancement in xylose reductase with simultaneous reduction of xylitol dehydrogenase activity by 22.9%. Later, the culture medium was optimized using statistical design and validated at shake flask and bioreactor level. Bioreactor studies affirmed the competence of mutant in xylitol accumulation. The xylitol titre and yield obtained with pure xylose were 98.9 g/L and 0.67 g/g, respectively while xylitol produced using non-detoxified xylose rich pre-hydrolysate from sugarcane bagasse was 79.0 g/L with an overall yield of 0.54 g/g. Conclusion: This study established the potential of P. fermentans in successfully valorising the hemicellulosic fraction for sustainable xylitol production.