One of the major bottlenecks of the biotechnological production of xylitol by pentose-fermenting yeasts is the presence of toxic compounds in the hemicellulosic hydrolysates, which inhibit the bioconversion of xylose into xylitol. In this work, short-term adaptation was evaluated as a strategy to minimize the toxicity of the sugarcane bagasse hemicellulosic hydrolysate to Candida guilliermondii FTI 20037. Yeast adaptation improved xylose assimilation as well as xylitol production. The beneficial effects of adaptation were more pronounced in the hydrolysate with higher concentration of toxic compounds, leading to an increase of 62.5% in the xylitol volumetric productivity in comparison to the use of non-adapted cells. In this condition, it was also verified the reduction of glycerol production (about 102%), a by-product formed as consequence of cellular stress, indicating a greater tolerance of adapted cells to the toxicity of hydrolysates. Short-term adaptation proved to be a promising strategy to improve considerably the microbial tolerance and overcome the toxicity of hydrolysates.

One of the major bottlenecks of the biotechnological production of xylitol by pentose-fermenting yeasts is the presence of toxic compounds in the hemicellulosic hydrolysates, which inhibit the bioconversion of xylose into xylitol. In this work, short-term adaptation was evaluated as a strategy to minimize the toxicity of the sugarcane bagasse hemicellulosic hydrolysate to Candida guilliermondii FTI 20037. Yeast adaptation improved xylose assimilation as well as xylitol production. The bene cial effects of adaptation were more pronounced in the hydrolysate with higher concentration of toxic compounds, leading to an increase of 62.5% in the xylitol volumetric productivity in comparison to the use of nonadapted cells. In this condition, it was also veri ed the reduction of glycerol production (about 102%), a by-product formed as consequence of cellular stress, indicating a greater tolerance of adapted cells to the toxicity of hydrolysates. Short-term adaptation proved to be a promising strategy to improve considerably the microbial tolerance and overcome the toxicity of hydrolysates.

No abstract

Aims Yeasts produce 2‐phenylethanol (2‐PE) from sugars via de novo synthesis; however, its synthesis is limited due to feedback inhibition on the isofunctional 3‐deoxy‐d‐arabino‐heptulosonate‐7‐phosphate (DAHP) synthases (Aro3p and Aro4p). This work aimed to select Kluyveromyces marxianus mutant strains with improved capacity to produce 2‐PE from sugars. Methods and Results Kluyveromyces marxianus CCT 7735 mutant strains were selected from UV irradiation coupled with screening of p‐fluoro‐dl‐phenylalanine (PFP) tolerant strains on culture medium without l‐Phe addition. Most of them produced 2‐PE titres higher than the parental strain and the Km_PFP41 mutant strain stood out for displaying the highest 2‐PE specific production rate. Moreover it showed higher activity of DAHP synthase than the parental strain. We sequenced both ARO3 and ARO4 genes of Km_PFP41 mutant and identified mutations in ARO4 which caused changes in both size and conformation of the Aro4p. These changes seem to be associated with the enhanced activity of DAHP synthase and improved production of 2‐PE exhibited by that mutant strain. Conclusions The Km_PFP41 mutant strain presented improved 2‐PE production via de novo synthesis and enhanced DAHP synthase activity. Significance and Impact of the Study The mutant strain obtained in this work may be exploited as a yeast cell factory for high‐level synthesis of 2‐PE.