Selection and directed evolution of yeasts - Identification and analysis of important metabolic pathways for application in the bioethanol and fermented beverage industries.

Abstract

SUMMARYThe ethanol and fermented-beverages industry has been demanding alternatives for increasing yields and reducing fermentation costs. In the bioethanol industry, temperature control along fermentation should be maintained around 30°C by heat exchangers that have a substantial cost and increase water consumption. To ferment properly at higher temperatures, yeast must be thermotolerant and resistant to the of stress conditions imposed during the production process. In the beer industry, strains with increased consumption of sugars such as maltose and maltotriose are constantly required. In this context, several technological applications using genetic and metabolic engineering have been employed. However, these modifications generate Genetically Modified Organisms (GMOs) that have restrictive regulations in their use, mainly in food products. The adaptive evolution technique becomes an excellent tool to modify yeast phenotypes. Since 2010, our research group has been working on the isolation of yeasts during the Brazilian bioethanol production that currently reaches 289 strains. The aim of this work is focus on the use of this strain library to identify strains with the desired characteristics by the industries to improve the fermentation process. Our initial results identified strains that belong to the Saccharomyces cerevisiae species by using a growth method in which the strains were inoculated in a solid medium using Lysine as the only Carbon source. Among the 289 isolates, we have identified 124 strains belonging to the S. cerevisiae species, with the identification of two strains with thermotolerant characteristics. However, these strains also need to be better adapted to increase the resistance to other stresses found during ethanol production. Preliminary results showed that these two strains showed an improvement in the fermentative performance and reproduction rates when induced in several cycles using high temperatures. Concerning beer production, we have been able to identify up to 60 yeasts with increase in maltose consumption, indicating a promising result for the evolution of these strains for application in the beer production. The development of these strains may have a direct application in fermentative processes aiming to increase the fermentative yields, improve quality as well as reduce costs and production time. We also aspire that our results could contribute significantly to the increment of industrial productive potential and the understanding of the metabolic pathways activated and repressed in these strains, contributing with important data for the scientific community. (AU)