Initial Investigation on Xylose Fermentation for Lignocellulosic Bioethanol Production

Abstract

Bioethanol production from lignocellulosic biomass has drawn tremendous attention, not only because bioethanol has a number of attractive traits as an alternative fuel to fossil fuel, but also due to attractive characteristics of lignocellulosic biomass as a feedstock. However, there is lack of a cost-competitive bioethanol production process since significant challenges exist, such as pretreatment of biomass feedstock, optimization of hydrolysis process, xylose fermentation and so on. In this work, we concentrate on the issue of xylose fermentation. Xylose is the second most abundant fermentable sugar in biomass hydrolysate, so its fermentation is essential for economic conversion of lignocellulose to bioethanol. However, the native strains of ethanol-producing microorganisms, such as S. cerevisiae, P. stipitis, E. coli and Z. mobilis, can not achieve effective cofermentation of glucose and xylose due to their intrinsic limitations. This thesis presents two potential routes for solving the xylose fermentation issue, modified single strain and co-culture. The basic idea of modified single strain is to engineer native strains to selectively produce bioethanol from glucose and xylose by the use of recombinant DNA techniques. The basic idea of co-culture on ethanol production is to utilize two different microbial strains in a system and enable one to ferment glucose, the other to ferment xylose stably and effectively. Current research status, difficulties and possible strategies about the two routes are depicted in details. Furthermore, valuable future research directions of the two routes are recommended. Through a broad and complete review, some initial investigation results are provided.