Xylitol Production by Candida tropicalis from Sugarcane Bagasse and Straw: an Adaptive Approach to Improve Fermentative Performance

The toxicity of hemicellulosic hydrolysates is one of the main bottlenecks of the biotechnological production of xylitol, as inhibitors released/generated during plant cell wall deconstruction impair xylitol production. Yeast adaptation can be applied to overcome this issue through the development of tolerant strains, improving microbial performance. Herein, we evaluated Candida tropicalis FTI20037 pre-cultivation in original, concentrated, and concentrated/detoxified sugarcane bagasse and straw hemicellulosic hydrolysate (SBSHH) to reduce hydrolysate’s toxicity during concentrated/detoxified SBSHH fermentations. Regarding glucose uptake, there were no differences between the evaluated conditions. In turn, lignocellulosic inhibitors negatively affected xylose uptake. The evaluated adaptive strategies did not improve xylose uptake at SBSHH fermentations. Xylitol production was also impaired by lignocellulosic inhibitors. However, pre-cultivation in concentrated/detoxified SBSHH increased xylitol yield and xylose-to-xylitol bioconversion efficiency by 13.3%, xylitol volumetric productivity by 7.1%, and xylitol specific production rate by 9.7%. A 21.5% reduction in glycerol production was also observed in this condition, indicating an increased tolerance to lignocellulosic inhibitors. Arabinose assimilation started slowly in all fermentations. Increased arabinose uptake rates were observed after xylose depletion, suggesting the existence of a carbon catabolite repression tendency between xylose and arabinose. Pre-cultivation in concentrated/detoxified SBSHH reduced this repression tendency, increasing arabinose consumption. Regarding lignocellulosic inhibitors, 5-HMF degradation was increased by pre-cultivation. No differences were observed for acetic acid and phenolic compounds consumption. The combination of SBSHH detoxification and C. tropicalis pre-cultivation was effective to improve xylitol production possibly due to the development of a more tolerant phenotype against SBSHH toxicity.