Breeding Of Acetic Acid Resistant Strains And Two Yeasts Cofermentation To Produce Ethanol

With the social development,world's demand for energy is increasing but traditional fossil energy is no-renewable,so it's urgent to find renewable eneigy.Lignocellulosic materials are renewable and can be used as the fermentation substrates for ethanol production.While,there are some problems remain in the cellulosic ethanol production,such as glucose repression and inhibitors repression.This study intends to take advantage of two strains cofermentation to remove the inhibition of xylose by glucose and accelerate the utilization rate of xylose.Meanwhile,atmospheric pressure room temperature plasma mutameter(ARTP)and fully automatic high-throughput microbial droplet culture instrument(MMC)were used to breed strains with the improvement of hydrolysis inhibitors tolerance.First,in order to relieve the inhibition of xylose by glucose,two strains cofermentations were carried out by Saccharomyces cerevisiae,which is capable of rapidly metabolizing glucose,and Spathaspora passalidarum,a strain capable of naturally utilizing xylose.The two strains cofermentations were carried under two different sugar concentration(high sugar concentration and low sugar concentration)conditions by changing the ratio of S.cerevisiae to S.passalidarum.The experiment results showed that the two strains cofermentations can relieve the inhibition of xylose utilization by glucose.Secondly,in order to reduce or even eliminate the influence of the inhibitors on the cell growth and fermentation performance,random mutagenesis of the strains in this study was carried out to increase the tolerance of inhibitors.Acetic acid is one of the main inhibitors,so,this study mainly aims to improve the acetic acid tolerance of the strains.S.passalidarum was induced mutation by atmospheric and room temperature plasma.Meanwhile,a fully automatic high-throughput microbial droplet culture instrument was used to screen the strain with manual screening methods.After multiple mutagenesis screenings,strains with improved resistance to the inhibitors were screened,and the obtained strains with improved tolerance were evaluated by cell growth investigation and fermentation experiments.The results showed that the strains obtained by mutagenesis screening could grow in a plate containing 5 g/L of acetic acid,which did improve the acetic acid tolerance.The results provided the reference for the improvement of acetic acid tolerance and also provided a strain for cellulosic bioethanol producing.