ARS | Publication request: Development of next generation biocatalyst for lower-cost ethanol production from lignocellulose

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 28, 2012
Publication Date: October 31, 2012
Citation: Liu, Z. 2012. Development of next generation biocatalyst for lower-cost ethanol production from lignocellulose. 8th International Symposium on Biocatalysis and Agricultural Biotechnology [abstract].

Technical Abstract: Economics of fermentation-based biotechnology rely extensively on microbial performance. For renewable ethanol production using lignocellulosic biomass feedstocks, two major technical challenges exist. First, inhibitory compounds liberated from lignocellulosic biomass pretreatment interfere with microbial growth and subsequent fermentations. Secondly, the traditional yeast used is limited in pentose conversion, which restricts efficient biomass sugar utilization, especially for pentoses which are rich in lignocellulose materials. Using systems biology approaches, we developed tolerant industrial yeast strains with competitive xylose utilization capabilities. The new yeast strains are able to in situ detoxify major biomass pretreatment inhibitors while producing ethanol. This technical advance eliminates inhibitor removal steps by physical, chemical or biological procedures thus reducing cost of cellulosic ethanol production. We synthesized a unique yeast xylose isomerase gene and genetically engineered it into the genome of the tolerant yeast by chromosomal integration to enable its xylose utilization. Genetic incorporation of heterologous xylose transporter genes in the industrial host strain further improved its xylose utilization efficiency and ethanol yield. These new genotypes are not only able to grow on xylose as sole carbon and energy source but also competitively ferment mixed sugars of glucose and xylose under oxygen limited conditions at significantly increased rates. Unlike commonly observed glucose repression on xylose utilization for genetically engineered yeast strains, the new genotypes displayed little diauxic lag in consumption of a mixture of glucose and xylose. Reprogrammed pathways for in situ detoxification involved in glycolysis and pentose phosphate pathways were uncovered and key mechanisms of the yeast tolerance illustrated. Challenges towards next generation biocatalyst development for advanced biofuels production will also be addressed.