Elucidation of the molecular bases of arabinose and xylose fermentation in Saccharomyces cerevisiae strains

• Grant number: 19/06942-4
• Support type: Scholarships in Brazil - Master
• Effective date (Start): December 01, 2019
• Effective date (End): November 30, 2021
• Field of knowledge: Biological Sciences - Genetics - Molecular Genetics and Genetics of Microorganisms
• Principal researcher: Leandro Vieira dos Santos
• Grantee: Paulo Emílio dos Santos Costa
• Home Institution: Centro Nacional de Pesquisa em Energia e Materiais (CNPEM). Ministério da Ciência, Tecnologia e Inovações (Brasil). Campinas , SP, Brazil

Abstract

Second generation (2G) ethanol represents the possibility of increasing the volume of ethanol produced in industry, without the need to increase the planted area of sugarcane, besides the sustainable destination to agricultural waste, such as sugarcane bagasse and straw. 2G ethanol is obtained from fermentation of sugars present in lignocellulosic biomass by yeast. The pre-treatment and enzymatic hydrolysis steps release the cellulosic fraction, basically composed with glucose and the hemicellulosic fraction, that contains sugars with six carbons and the pentoses D-xylose and L-arabinose. Glucose is rapidly metabolized to ethanol by the yeast Saccharomyces cerevisiae. However, wild strains of this organism are unable to ferment pentoses. As these sugars represent a large fraction of the lignocellulosic biomass, metabolic engineering procedures and adaptive evolution are necessary to obtain genetically modified strains of this yeast capable of fermenting pentoses. Our group previously developed an industrial strain from S. cerevisiae PE-2, with efficient fermentation of D-xylose in 2G ethanol. The next step in developing more efficient yeasts for second-generation ethanol is the heterologous expression of L-arabinose catabolism genes. Thus, the aim of the work is the development of a modified strain of S. cerevisiae capable of fermenting the pentoses L-arabinose and D-xylose, aiming at the production of second generation ethanol. The genes coding for L-arabinose isomerase, L-ribuloquinase and L-ribulose-5-phosphate-4-epimerase will be inserted into an efficient xylose fermentation strain. After adaptive evolution procedures, whole-genome sequencing of the evolved strains will allow the identification of the mutations fixed in population during the evolution process, responsible for the metabolism of the two pentoses. There are no reports in literature of the identification of molecular bases that allow the efficient assimilation of arabinose in S. cerevisiae. The elucidation of molecular mechanisms that regulates the efficient assimilation and fermentation of arabinose and xylose in S. cerevisiae is an essential step in the development and viability of second generation ethanol technology. The efficient use of all biomass sugars is fundamental to increase economic viability and minimize environmental impacts in second generation ethanol production. (AU)