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Improving the Response of Saccharomyces cerevisiae to Lignocellulosic Hydrolysate Inhibitors in Ethanolic Fermentation

Almeida, Joao LU (2009)
Abstract
The production of ethanol based on lignocellulosic biomass requires the fermentation of a hydrolysate containing hexose and pentose sugars in an inhibitory environment. In fact, the lignocellulosic hydrolysate obtained from pretreatment and hydrolysis of the raw material contains a variety of inhibitory compounds, including (i) the furaldehydes 5-hydroxymethyl-2-furaldehyde (HMF) and 2-furaldehyde (furfural), (ii) weak acids (e.g. acetic acid) and (iii) phenolic compounds. These compounds reduce ethanol yield and the specific ethanol productivity, extend the lag phase, and reduce the growth rate and viability of microorganisms.

In this work, the enzymes ADH6, mut-ADH1 and XR were identified as being responsible for NADPH-, NADH-,... (More)
The production of ethanol based on lignocellulosic biomass requires the fermentation of a hydrolysate containing hexose and pentose sugars in an inhibitory environment. In fact, the lignocellulosic hydrolysate obtained from pretreatment and hydrolysis of the raw material contains a variety of inhibitory compounds, including (i) the furaldehydes 5-hydroxymethyl-2-furaldehyde (HMF) and 2-furaldehyde (furfural), (ii) weak acids (e.g. acetic acid) and (iii) phenolic compounds. These compounds reduce ethanol yield and the specific ethanol productivity, extend the lag phase, and reduce the growth rate and viability of microorganisms.

In this work, the enzymes ADH6, mut-ADH1 and XR were identified as being responsible for NADPH-, NADH-, and NAD(P)H-dependent HMF and furfural reduction, respectively, in yeast. The tolerance and fermentation rates of Saccharomyces cerevisiae laboratory strains on defined medium and/or on lignocellulosic hydrolysate were improved by overexpression of the genes encoding for these enzymes. It was also shown that overexpression of furaldehyde reductases benefits product distribution in recombinant xylose-utilizing S. cerevisiae strains carrying the xylose reductase/xylitol dehydrogenase pathway during xylose fermentation. Finally, strains with higher furaldehyde conversion rates were shown to grow faster and ferment lignocellulosic hydrolysates faster.

Evaluation of industrial strains of S. cerevisiae showed that the selection of a robust strain and its evaluation under representative conditions are essential for lignocellulosic hydrolysate fermentation, since strains perform differentially depending on the hydrolysate and the conditions employed. The use of fed-batch mode is advantageous not only because the inhibitors are kept at low concentrations and the capacity of the yeast to convert them is not surpassed, but also because it allows cells to adapt to the inhibitors in the lignocellulosic hydrolysate. Indeed, using microarray analysis, and in vitro and in vivo activity measurements it was demonstrated that short-term adaptation of the yeast to lignocellulosic hydrolysate increased detoxifying activities and induced the expression of genes related to the repair of cellular damage. The results presented in this work show that integration of process design and strain improvement strategies could be used to improve the yeast performance in ethanolic fermentation of lignocellulosic hydrolysates. (Less)
Please use this url to cite or link to this publication:
author
supervisor
opponent
  • Professor François, Jean Marie, University of Toulouse, France
organization
publishing date
type
Thesis
publication status
published
subject
keywords
furfural, ethanol, fermentation, phenolics, furaldehyde, HMF, ADH1, xylose reductase, tolerance, Saccharomyces cerevisiae, Lignocellulosic hydrolysate inhibitors, ADH6
pages
200 pages
publisher
Division of Applied Microbiology
defense location
Lecture hall B, Center for Chemistry and Chemical Engineering, Getingevägen 60, Lund University Faculty of Engineering
defense date
2009-04-17 10:00
ISBN
978-91-628-7722-4
language
English
LU publication?
yes
id
219c8f59-6e7c-40f2-b075-06cf592b304f (old id 1361277)
date added to LUP
2009-03-23 12:58:36
date last changed
2016-09-19 08:45:05
@misc{219c8f59-6e7c-40f2-b075-06cf592b304f,
  abstract     = {The production of ethanol based on lignocellulosic biomass requires the fermentation of a hydrolysate containing hexose and pentose sugars in an inhibitory environment. In fact, the lignocellulosic hydrolysate obtained from pretreatment and hydrolysis of the raw material contains a variety of inhibitory compounds, including (i) the furaldehydes 5-hydroxymethyl-2-furaldehyde (HMF) and 2-furaldehyde (furfural), (ii) weak acids (e.g. acetic acid) and (iii) phenolic compounds. These compounds reduce ethanol yield and the specific ethanol productivity, extend the lag phase, and reduce the growth rate and viability of microorganisms. <br/><br>
In this work, the enzymes ADH6, mut-ADH1 and XR were identified as being responsible for NADPH-, NADH-, and NAD(P)H-dependent HMF and furfural reduction, respectively, in yeast. The tolerance and fermentation rates of Saccharomyces cerevisiae laboratory strains on defined medium and/or on lignocellulosic hydrolysate were improved by overexpression of the genes encoding for these enzymes. It was also shown that overexpression of furaldehyde reductases benefits product distribution in recombinant xylose-utilizing S. cerevisiae strains carrying the xylose reductase/xylitol dehydrogenase pathway during xylose fermentation. Finally, strains with higher furaldehyde conversion rates were shown to grow faster and ferment lignocellulosic hydrolysates faster. <br/><br>
Evaluation of industrial strains of S. cerevisiae showed that the selection of a robust strain and its evaluation under representative conditions are essential for lignocellulosic hydrolysate fermentation, since strains perform differentially depending on the hydrolysate and the conditions employed. The use of fed-batch mode is advantageous not only because the inhibitors are kept at low concentrations and the capacity of the yeast to convert them is not surpassed, but also because it allows cells to adapt to the inhibitors in the lignocellulosic hydrolysate. Indeed, using microarray analysis, and in vitro and in vivo activity measurements it was demonstrated that short-term adaptation of the yeast to lignocellulosic hydrolysate increased detoxifying activities and induced the expression of genes related to the repair of cellular damage. The results presented in this work show that integration of process design and strain improvement strategies could be used to improve the yeast performance in ethanolic fermentation of lignocellulosic hydrolysates.},
  author       = {Almeida, Joao},
  isbn         = {978-91-628-7722-4},
  keyword      = {furfural,ethanol,fermentation,phenolics,furaldehyde,HMF,ADH1,xylose reductase,tolerance,Saccharomyces cerevisiae,Lignocellulosic hydrolysate inhibitors,ADH6},
  language     = {eng},
  pages        = {200},
  publisher    = {ARRAY(0x79db120)},
  title        = {Improving the Response of Saccharomyces cerevisiae to Lignocellulosic Hydrolysate Inhibitors in Ethanolic Fermentation},
  year         = {2009},
}