Tuesday, April 30, 2013
Exhibit Hall
Marine plant biomass is a renewable feedstock that can be used for producing fuels and chemicals and has many advantages over terrestrial biomass from food or lignocellulosic materials. Galactose is the major sugar obtained from hydrolysis of some marine biomass, such as red seaweed. Although Saccharomyces cerevisiae is capable of growing on galactose, the ethanol yield and productivity from galactose fermentation are considerably lower than those from glucose fermentation. In this study, systematic and combinatorial approaches were combined to develop an engineered S. cerevisiae strain with higher ethanol yield and productivity from galactose. Deletion of a novel gene identified by a model-based approach led to a metabolic death valley, i.e. no galactose fermentation. However, the metabolic death valley was a necessary intermediate phenotype to reach optimal galactose fermentation rapidly through evolutionary engineering by serial subculture in galactose media. The resulting strain obtained through both rational and combinatorial engineering was able to produce ethanol with an 81% increase in yield and 4.7-fold improvement in volumetric productivity as compared to the wild-type strain. Genome sequencing was used to identify SNPs responsible for the phenotype of this super galactose fermenting strain. In addition, a metabolomics study was used to further characterize putative mechanisms underlying the fast galactose fermenting phenotype at both molecular and systems levels. The results in this study demonstrate a promising approach for improving galactose fermentation in S. cerevisiae and can be applied for the industrial production of bioethanol from red seaweed, cheese whey, molasses, or other renewable sources containing galactose.