13C-metabolic flux analysis of fermentation in a xylose/glucose mixture substrate by yeasts Scheffersomyces stipitis NRRL Y-7124 and Spathaspora passalidarum NRRL Y-27907

• Grant number: 17/21634-9
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate (Direct)
• Start date: January 22, 2018
• End date: December 21, 2018
• Field of knowledge: Engineering - Chemical Engineering - Chemical Process Industries
• Principal Investigator: Aline Carvalho da Costa
• Grantee: Luiz Eduardo Biazi
• Supervisor: Pau Ferrer Alegre
• Host Institution: Faculdade de Engenharia Química (FEQ). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil
• Institution abroad: Universitat Autònoma de Barcelona (UAB), Spain
• Associated to the scholarship: 16/14567-0 - Mathematical modeling of second generation bioethanol production with cell recycle by using the microorganisms Scheffersomyces stipitis and Spathaspora passalidarum, BP.DD

Abstract

Considering the process of ethanol production from lignocellulosic biomass (second-generation bioethanol), microorganisms that are naturally capable of converting pentoses into ethanol are desired, once fermentation with wild strains is simpler and cheaper than fermentation with transformed strains. In this scenario, two non-conventional yeasts have the potential for industrial application in the production of ethanol from hydrolysates that are rich in pentoses: Scheffersomyces stipitis and Spathaspora passalidarum.Although these yeasts are both able to ferment pentose sugars, they have different metabolism when submitted to the same conditions. While S. stipitis requires accurately controlled microaerophilic condition during xylose fermentation, rendering the process technically difficult and expensive, recent works on literature reported that S. passalidarum had high ethanol production yield, fast cell growth and rapid sugar consumption under strictly anaerobiosis. Although S. passalidarum performs high yield in ethanol production from xylose under anaerobic conditions, it's reported that the presence of glucose interferes on xylose metabolism, requiring microaeration. In first-generation Brazilian ethanol mills (from sugarcane juice), oxygen transfer has never been precisely monitored to address the real benefit of this variable. In this context, the capacity of converting xylose into ethanol under anaerobiosis becomes a differential in the selection of a microorganism for a cost-efficient lignocellulosic ethanol production process.One strategy to investigate the mentioned differences between S. stipitis and S. passalidarum is the use of 13C-Metabolic Flux Analysis (13C-MFA), where carbon isotopes are used to trace the cell metabolism. This technology has been continuously developed and widely applied to investigate cell metabolism and quantify the carbon flux distribution, becoming a valuable tool to provide rigorous and quantitative readouts of in vivo network-scale metabolic behaviors. Metabolic Flux Analysis has been extensively applied, including the quantifcation of metabolic fluxes, in glucose-consuming yeasts and, more recently, in natural xylose-utilizing yeasts, as well as genetically engineered S. cerevisiae. With the information provided by this tool, it's possible to create structured mathematical models to describe biochemical reactions regarding xylose fermentation metabolism that could be used to optimize microorganism transformation.In contribution to the research line that takes place at Brazilian Bioethanol Science and Technology Laboratory (CTBE), where fermentations have been extensively executed to understand the behavior and the kinetic parameters regarding S. stipitis and S. passalidarum, and to the extensive research in mathematical modelling of bioprocesses developed at University of Campinas (UNICAMP), leading to significant advances in lignocellulosic bioethanol technology, this project aims to apply 13C-MFA during a xylose/glucose mixture fermentation under different oxygen concentration conditions for both yeasts, in collaboration with Laboratory of Metabolic Engineering and Applied Systems Biology, from Universitat Autònoma de Barcelona (UAB), where this tool have been applied in similar cases. Through the results obtained with this technology, it will be possible to address the effects of glucose and oxygen concentration (anaerobiosis and microaeration) on xylose fermentation metabolism of S. stipitis and S. passalidarum. (AU)