Molecular Mechanism of d-Xylitol Production in Yeasts: Focus on Molecular Transportation, Catabolic Sensing and Stress Response

Abstract

Xylitol is a naturally occurring non fermentable sugar alcohol. It can be produced by the microbial fermentation of xylose extracted from hemicellulose of lignocellulosic substrates like corn fiber, corn husk, sugarcane bagasse and birch wood. In last few decades, xylitol gained significant importance due to its applications in food and pharmaceutical industries. Sustainable production of xylitol from renewable sources is possible by fermentation process using xylose assimilating microbes. As chemical production of xylitol involves high temperature, pressure and expensive purification steps, highly efficient biotechnological production of xylitol using microorganisms is gaining more interest over chemical processes. For the economic production of xylitol, microorganisms with high osmotolerance, inhibitor resistance, fast conversion rates, and stress tolerance are required in the fermentation process. As xylose uptake might be a limiting factor for xylose fermentation, the study of xylose uptake with respect to xylose transporting proteins and improvement of utilization of sugar mixtures is necessary. This review is to provide an overall view of xylitol production by yeast strains under sugar, saline and different nutritive stress conditions. In addition this review emphasizes the role of molecular changes (genes) and pathways involved in the utilization and transport of sugars for increased xylitol production.