Pentose fermentation is an essential step to improve yield of ethanol and organic acid production from plant biomass. In view of this, many efforts have been directed to the hydrolysis of hemicellulosic material and the consequent fermentation of D-xylose derived from this process. However, studies in metabolic engineering have shown that Saccharomyces cerevisiae, even when modified for pentose assimilation, has not presented satisfactory industrial yield. On the other hand, some non-Saccharomyces yeasts have been shown to be able to assimilate xylose. It is agreed that pentose assimilation and microbial growth using these sugars imply an efficient membrane transport system. Thus, studying different yeasts for their ability to assimilate xylose has been a strategy to understand the metabolism of this sugar and support future studies of metabolic engineering for the S. cerevisiae industrial line. Recent studies have shown differences in the expression of xylose transporters according to the pH of the culture medium. In general, xylose transport is carried out by H + transport, and thus the motive proton force directly interferes with transport efficiency. Based on preliminary studies, we note that the yeasts we are going to study are able to grow on xylose medium. For this reason, in this project we propose to investigate for 96 h of cultivation the capacity of xylose assimilation by these yeasts, they are: Candida quercitrusa N20, Trichosporon laibachii and Aureobasidium pullulans LB3.1. Microbial culture will be evaluated in media containing xylose as the only sugar source at initial pH 4,5 and 6,5. Yeast tolerance to hydroxymethylfurfural, furfural, ferulic acid and vanillin inhibitors will also be evaluated. This project of scientific initiation is of great contribution for future studies where the transport kinetics can be analyzed. This research will support future studies of metabolic engineering with the purpose of capacitating the Saccharomyces cerevisiae industrial strain.
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