Stepwise metabolic engineering of Candida tropicalis for efficient xylitol production from xylose mother liquor

Lihua Zhang,Wei Shen,Xianzhong Chen,Qi Li,Junhua Wang,Zhen Chen

doi:10.1186/s12934-021-01596-1

Abstract

BackgroundCommercial xylose purification produces xylose mother liquor (XML) as a major byproduct, which has become an inexpensive and abundant carbon source. A portion of this XML has been used to produce low-value-added products such as caramel but the remainder often ends up as an organic pollutant. This has become an issue of industrial concern. In this study, a uracil-deficient Candida tropicalis strain was engineered to efficiently convert XML to the commercially useful product xylitol.ResultsThe xylitol dehydrogenase gene was deleted to block the conversion of xylitol to xylulose. Then, an NADPH regeneration system was added through heterologous expression of the Yarrowia lipolytica genes encoding 6-phosphate-gluconic acid dehydrogenase and 6-phosphate-glucose dehydrogenase. After process optimization, the engineered strain, C. tropicalis XZX-B4ZG, produced 97.10 g L− 1 xylitol in 120 h from 300 g L− 1 XML in a 5-L fermenter. The xylitol production rate was 0.82 g L− 1 h− 1 and the conversion rate was 92.40 %.ConclusionsIn conclusion, this study performed a combination of metabolic engineering and process optimizing in C. tropicalis to enhance xylitol production from XML. The use of C. tropicalis XZX-B4ZG, therefore, provided a convenient method to transform the industrial by-product XML into the useful material xylitol.

Highlights

Commercial xylose purification produces xylose mother liquor (XML) as a major byproduct, which has become an inexpensive and abundant carbon source
Analysis of the XML used in this study The chemical composition of XML varies widely depending on the corn cob hydrolysis and crystallization processes used during xylose production [1]
Reports have stated that furfural can seriously suppress the growth of many microorganisms [13, 18], we found that C. tropicalis XZX could grow at a rapid rate, consistent with previous studies showing that C. tropicalis is tolerance to these compounds [18]

Summary

Introduction

Commercial xylose purification produces xylose mother liquor (XML) as a major byproduct, which has become an inexpensive and abundant carbon source. A portion of this XML has been used to produce low-valueadded products such as caramel but the remainder often ends up as an organic pollutant This has become an issue of industrial concern. The xylose used in this process is generally extracted from the acid hydrolysate of hemicellulose obtained from sources such as corncob and sugarcane bagasse [2] This acid hydrolysate contains many other sugars and impurities that complicate xylose purification and lead to the production of xylose mother liquor (XML) as the major by-product of. Other microbial processes have been used to convert XML to high-value chemicals such as xylitol [1, 6], solvents [3, 9], welan gum [10] and succinic acid [7]. There is an urgent need for simpler biotechnological systems that can improve the value of XML

Methods

Results

Conclusion