Direct bioethanol production from wheat straw using xylose/glucose co-fermentation by co-culture of two recombinant yeasts

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Web End = J Ind Microbiol Biotechnol (2017) 44:453464 DOI 10.1007/s10295-016-1893-9

BIOENERGY/BIOFUELS/BIOCHEMICALS - ORIGINAL PAPER

Direct bioethanol production from wheat straw using xylose/ glucose cofermentation by coculture of two recombinant yeasts

Yuanyuan Zhang1 Caiyun Wang1 Lulu Wang1 Ruoxin Yang1 Peilei Hou1 Junhong Liu1

Received: 8 August 2016 / Accepted: 22 December 2016 / Published online: 18 January 2017 Society for Industrial Microbiology and Biotechnology 2017

Introduction

Lignocellulosic materials, such as agricultural (e.g., corn stover, wheat straw, sugarcane bagasse, etc.) and forestry residues (e.g., hardwoods/softwoods, etc.), waste paper, and industrial wastes, are the most abundant, cheap and renewable biomass resources on the earth [7]. Bioethanol production from lignocellulosic biomasses instead of grain resources may provide an ideal alternative fuel source in the future [12, 27]. Lignocellulosic biomass in general consists of 4050% cellulose, 2530% hemicellulose and 1520% lignin [34]. The cellulose and hemicellulose are polysaccharides that can be hydrolyzed to hexoses and pentoses; however, the lignin which is a phenol compound cannot be used for ethanol production. Ethanol production from these raw materials consists of three main steps: pre-treatment of biomass, enzymatic hydrolysis of cellulose and hemicellulose to release fermentable hexoses and pentoses, and fermentation of the resulting sugars. Three different types of enzymes, namely, endoglucanase (EG, EC 3.2.1.4), exoglucanase or cellobiohydrolase (CBH, EC 3.2.1.91), and -glucosidase (BGL, EC 3.2.1.21) are necessary for hydrolysis of cellulose to glucose [28]. Xylan is the major constituent of hemicellulose and is a heteropolysaccharides with a homopolymeric backbone of -D-xylose [20]. Xylose is the main pentose and second major fermentable sugar after glucose in lignocellulosic feedstocks. The hydrolysis of xylan to xylose requires the synergetic action of endoxylanase (EC 3.2.1.8) and -xylosidase (EC 3.2.1.37). The yield of ethanol fermentation can be increased 25% by making full use of the xylose fermentation in lignocellulosic materials to produce ethanol, so its fermentation is essential for the economic conversion of lignocellulose to ethanol [3]. The cost-effective and efcient industrial bioconversion of lignocellulosic feedstocks

Abstract To achieve a cost-effective bioconversion of lignocellulosic materials, a novel xylose/glucose co-fermentation process by co-culture of cellulose-utilizing recombinant Saccharomyces cerevisiae (S. cerevisiae) and xylan-utilizing recombinant Pichia pastoris (P. pastoris) was developed, in which ethanol was produced directly from wheat straw without additional hydrolytic enzymes. Recombinant S. cerevisiae coexpressing...