Microorganisms for Xylitol Production: Focus on Strain Improvement

Abstract

Xylitol, a five-carbon sugar alcohol, is widely used as a functional sweetener in the food and confectionary industry because of a number of advantageous properties. Although xylitol is industrially produced by chemical reduction of d-xylose derived from hemicellulose hydrolysates, this production method is uneconomical because of the requirement for pure d-xylose, high temperature, and pressure. Therefore, xylitol production by microorganisms has attracted focus as an economical and environment-friendly method. A variety of compounds have been used as substrates (d-xylose, d-glucose, d-arabitol, and l-arabinose) or co-substrates (d-glucose, ethanol, and glycerol) during microbial production of xylitol. In order to improve the biological production of xylitol, both natural xylitol-producing and nonproducing strains of microorganisms have been subjected to genetic modification strategies. This chapter describes recent advances made in metabolic engineering efforts aimed at improving production of xylitol by fungi, yeasts, and bacteria.