Isolation and characterization of xylitol-producing yeasts from the gut of colleopteran insects

A total of 35 yeasts were isolated from the gut of beetles collected from Hyderabad city, India. Twenty of these yeasts utilized xylose as a sole carbon source but only 12 of these converted xylose to xylitol. The ability to convert xylose to xylitol varied among the isolates and ranged from 0.12 to 0.58 g/g xylose. Based on the phenotypic characteristics and phylogenetic analysis of the D1/D2 domain sequence of 26S rRNA gene, these isolates were identified as members of Pichia, Candida, Issatchenkia, and Clavispora. Strain YS 54 (CBS 10446), which was phylogenetically similar to Pichia caribbica and which formed hat-shaped ascospore characteristics of the genus Pichia, was the best xylitol producer (0.58 g xylitol/g xylose). YS 54 was also capable of producing xylitol from sugarcane bagasse hydrolysate and the efficiency of conversion was 0.32 g xylitol/g xylose after 20 cycles of adaptation in medium containing sugarcane bagasse hydrolysate.