MASTER THESIS PROJECT
INDUSTIAL BIOTECHNOLOGY
INCREASED ACETIC ACID TOLERANCE IN SACCHAROMYCES
CEREVISIAE BY MEMBRANE ENGINEERING
Duration: 6-12 months (30-60 ECTS)
Contact person: Lina Lindberg (lina.lindberg@chalmers.se)
The earth’s resources are limiting and a shift from fossil hydrocarbon raw materials to the use of renewable
alternatives for production of fuels, chemicals and materials is a requirement for a sustainable future.
Lignocellulosic biomass is considered a promising raw material due to its high abundance in nature and to
the fact that it does not compete with food crops. The yeast Saccharomyces cerevisiae is the number one
organism evaluated for fermentation of lignocellulosic material due to the its high cellular robustness, high
production titers of ethanol, and the experience we have, deriving from the widespread use in already
existing industrial processes.
When lignocellulosic biomass is decomposed into monomeric sugars available for the yeast to ferment,
acetyl groups are also released resulting in high concentrations of acetic acid in the raw material. Acetic acid
is toxic for the yeast cell and is considered one of the major hurdles preventing an economical process using
lignocellulosic biomass. The exact mechanism of acetic acid toxicity is unknown, but the protonated form of
acetic acid enters the cell over the plasma membrane and causes a lot of harm inside the cell.
This project aims at avoiding the toxic effect of acetic acid by preventing its entrance into the cell.
The effect will be obtained by genetic engineering and in particular by engineering the plasma membrane
lipid composition in order to decrease the membrane permeability for acetic acid. Zygosaccharomyces bailii,
a yeast very tolerant to acetic acid has been studied and it has given us clues on how to change the plasma
membrane lipid composition in order to achieve decreased acetic acid permeability (Lindberg et al. (2013)
Lipidomic Profiling of Saccharomyces cerevisiae and Zygosaccharomyces bailii Reveals Critical Changes
in Lipid Composition in Response to Acetic Acid Stress. PLoS ONE 8(9): e73936).
This master thesis project aims at genetically engineer the desired changes into Saccharomyces
cerevisiae as well as evaluating the effect of those changes in terms of membrane lipid composition,
cellular physiology and acetic acid tolerance.
The following techniques will be applied in the project:
METABOLIC ENGINEERING
- Gene overexpression, gene deletion, insertion of heterologous genes, posttranslational modifications
or directed amino acid changes to particular enzymes
PHYSIOLOGICAL CHARACTERIZATION OF NEW STRAINS
- Growth evaluation using bioreactors
- Metabolic analysis using HPLC and IC
ANALYSIS OF MEMBRANE LIPID COMPOSITION
- Lipidomic profiling using MRM-MS (in
collaboration with University of Geneva)
CHALMERS UNIVERSITY OF TECHNOLOGY