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Type:	Tese
Title:	Diversity, evolution, and adaptation of yeasts able to assimilate and ferment lignocellulose-related sugars
Authors:	Katharina de Oliveira Barros
First Advisor:	Carlos Augusto Rosa
First Co-advisor:	Chris Todd Hittinger
First Referee:	Daniel de Assis Santos
Second Referee:	Boris Stambuk
Third Referee:	Marc-André Lachance
metadata.dc.contributor.referee4:	Dana Opulente
Abstract:	Production of ethanol, other fuels and chemicals from lignocellulosic materials depend on efficient D-xylose conversion. Novel xylose-fermenting yeasts species, including the ones assigned to the genera Spathaspora and Scheffersomyces, have been described and are potential sources of genes to improve xylose fermentation in Saccharomyces cerevisiae. Therefore, the aims of this study were to isolate, identify, and characterize the diversity of yeasts able to assimilate lignocellulosic sugars, study the factors behind the xylose fermentation by Spathaspora and Scheffersomyces species to understand the different behaviours presented by them, and develop a strain of Spathaspora passalidarum able to grow in sugarcane bagasse hydrolysate to investigate the genetic basis of the adaptation. A total of 569 yeast strains were isolated from 60 rotting wood samples collected in three areas of Brazilian Amazonian rainforest. Diversity analyses indicate a dryland forest as the most diverse area and Carú, a floodplain forest, as the least. Of the 89 species identified, 52 were previously known and 37 were new. Sugiyamaella was the most prevalent genus identified, followed by Kazachstania. Schwanniomyces polymorphus, Scheffersomyces amazonensis, and Wickerhamomyces edaphicus were the most frequently isolated yeast species. Xylose fermentation assays performed with Scheffersomyces and Spathaspora species under different aeration conditions exhibited Scheffersomyces parashehatae, Scheffersomyces xylosifermentans, and Sp. passalidarum as remarkable xylose fermenters under moderate aeration condition. They achieved the highest yields of ethanol among the species tested. However, the determination of enzyme activities and cofactors usage of xylose reductase (XR) and xylitol dehydrogenase (XDH) combined with the fermentation results revealed the great negative impact of the high aeration on the xylose catabolism in these species. The findings also indicate that the degree of the enzyme affinity by the cofactor is extremely important for the generation of ethanol. In the third part of this work, ultraviolet-induced mutagenesis followed by adaptive laboratory evolution (ALE) were undertaken to adapt Sp. passalidarum to the inhibitors present in hydrolysates, especially acetic acid. The mutant MT01 showed improved growth in defined medium with xylose and acetic acid. It was subjected to ALE and the evolved strains ME3.5.5 and MEH30.1 were able to grow in sugarcane bagasse hydrolysate (SBHH). Four genes contain disruptive heterozygous mutations, including CYR1 that encodes adenylate cyclase, and they are candidates for causing increased growth in SBHH.
Subject:	Microbiologia Leveduras Xilose Fermentação Spathaspora passalidarum Lignocelulose
language:	eng
metadata.dc.publisher.country:	Brasil
Publisher:	Universidade Federal de Minas Gerais
Publisher Initials:	UFMG
metadata.dc.publisher.department:	ICB - DEPARTAMENTO DE MICROBIOLOGIA
metadata.dc.publisher.program:	Programa de Pós-Graduação em Microbiologia
Rights:	Acesso Restrito
URI:	http://hdl.handle.net/1843/38492
Issue Date:	5-Aug-2021
metadata.dc.description.embargo:	5-Aug-2023
Appears in Collections:	Teses de Doutorado

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