Model-based optimization of Scheffersomyces stipitis and Saccharomyces cerevisiae co-culture for efficient lignocellulosic ethanol production

Pornkamol Unrean,Sutamat Khajeeram

doi:10.1186/s40643-015-0069-1

Abstract

The utilization of both C6 and C5 sugars is required for economical lignocellulosic bio-based processes. A co-culture system containing multiple strains of the same or different organisms holds promise for conversion of the sugar mixture available in different lignocellulosic feedstock into ethanol. Herein a co-culture kinetic model has been developed which can describe the co-cultivation of S. stipitis and S. cerevisiae for ethanol fermentation in mixed C6/C5 sugars. The predicted fermentation kinetics and ethanol production performance agreed well with experimental results, thus validating the model. The co-culture kinetic model has been implemented to design the optimal cell ratio for efficient conversion of rice straw or sugarcane bagasse feedstock into ethanol. The results reveal that the optimal co-culture system could enhance ethanol titer by up to 26 %, and ethanol productivity by up to 29 % compared to a single-strain culture. The maximum ethanol titer and productivity reached by the optimized co-culture was 46 and 0.49 g/l h, respectively. The co-culture model described here is a useful tool for rapid optimization of S. stipitis/S. cerevisiae co-culture for efficient and sustainable lignocellulosic ethanol production to meet the economic requirements of the lignocellulosic ethanol industry. The developed modeling tool also provides a systematic strategy for designing the optimal cell ratio of co-culture, leading to efficient fermentation of the C6/C5 sugars available in any biomass feedstock.

Highlights

The utilization of both C6 and C5 sugars is required for economical lignocellulosic bio-based processes
Since the consumption of C6/C5 sugar mixture depends on the composition of the two strains used in the culture, the optimal cell ratio of co-culture can be varied with varying composition of sugars available in different sources of biomass feedstock
Development of co‐culture kinetic modeling Mixed culture of S. stipitis and S. cerevisiae can be used to selectively adjust the fermentation kinetics of mixed C6/C5 sugars resulting in an optimal co-fermentation of the sugar mixture

Summary

Introduction

The utilization of both C6 and C5 sugars is required for economical lignocellulosic bio-based processes. The economic success of lignocellulose-based ethanol production would, require a culture system able to handle the variation of sugar composition and efficiently ferment the sugar mixture into ethanol at high titer and productivity to meet the technical and economic requirements of the ethanol industry. Unlike the single-strain culture, the co-culture containing two C6- and C5-fermenting strains can be adjusted in the cell inoculum ratio of each strain used for efficient ethanol fermentation. This makes the co-culture an adjustable system to efficiently ferment C6/C5 sugar mixture at minimal fermentation time and at high titer and productivity, thereby resulting in less production time and cost

Methods

Results

Conclusion