Boosting Ethanol Productivity of Zymomonas mobilis 8b in Enzymatic Hydrolysate of Dilute Acid and Ammonia Pretreated Corn Stover Through Medium Optimization, High Cell Density Fermentation and Cell Recycling.

Ying Li,Zhihua Liu,Mingjie Jin,Rui Zhai,Xiaoxiao Jiang,Xinchuan Yuan,Xiangxue Chen

doi:10.3389/fmicb.2019.02316

Ying Li, Zhihua Liu + Show 5 more

Open Access

https://doi.org/10.3389/fmicb.2019.02316

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Abstract

The presence of toxic degradation products in lignocellulosic hydrolysate typically reduced fermentation rates and xylose consumption rate, resulting in a decreased ethanol productivity. In the present study, Zymomonas mobilis 8b was investigated for high cell density fermentation with cell recycling to improve the ethanol productivity in lignocellulosic hydrolysate. The fermentation performances of Z. mobilis 8b at various conditions were first studied in yeast extract-tryptone medium. It was found that nutrient level was essential for glucose and xylose co-fermentation by Z. mobilis 8b and high cell density fermentation with cell recycling worked well in yeast extract-tryptone medium for 6 rounds fermentation. Z. mobilis 8b was then studied in enzymatic hydrolysates derived from dilute acid (DA) pretreated corn stover (CS) and ammonia pretreated CS for high cell density fermentation with cell recycling. Ethanol productivity obtained was around three times higher compared to traditional fermentation. Ethanol titer and metabolic yield were also enhanced with high cell density fermentation. Z. mobilis 8b cells showed high recyclability in ammonia pretreated CS hydrolysate.

Highlights

Bioconversion of lignocellulosic biomass to ethanol has drawn great attention because of its benefit to environmental, economic, and social sustainability
We have demonstrated high cell density fermentation with cell recycling on S. cerevisiae (Jin et al, 2012, 2016) and preliminary found the great potential of this strategy on Z. mobilis 8b
Based on the fermentation performances of Z. mobilis 8b, we designed and investigated high cell density fermentation with cell recycling in both synthetic medium and lignocellulosic hydrolysate derived from dilute acid (DA) and ammonia pretreated corn stover (CS)

Summary

INTRODUCTION

Bioconversion of lignocellulosic biomass to ethanol has drawn great attention because of its benefit to environmental, economic, and social sustainability. To obtain sugar streams from lignocellulosic biomass for fermentation, a pretreatment is needed to break up the lignocellulose and enzymatic hydrolysis is required to degrade the polysaccharide into fermentable monosaccharides, such as glucose and xylose (Lai et al, 2019) Many pretreatment strategies such as dilute acid (DA) (Zhai et al, 2018; Huang et al, 2019), dilute alkali (McIntosh and Vancov, 2011), steam explosion (Liu and Chen, 2017; Zhong et al, 2019), liquid hot water (Zhuang et al, 2016; Tian et al, 2019), ammonia fiber expansion (Serate et al, 2015; Jin et al, 2016), and extractive ammonia pretreatment (Sousa et al, 2016) have been developed to deconstruct the lignocellulose to improve their hydrolysablity by cellulases. Based on the fermentation performances of Z. mobilis 8b, we designed and investigated high cell density fermentation with cell recycling in both synthetic medium and lignocellulosic hydrolysate derived from DA and ammonia pretreated corn stover (CS)

MATERIALS AND METHODS

Analysis Methods

RESULTS AND DISCUSSION

DATA AVAILABILITY STATEMENT