Abstract
BackgroundDuring industrial fermentation of lignocellulose residues to produce bioethanol, microorganisms are exposed to a number of factors that influence productivity. These include inhibitory compounds produced by the pre-treatment processes required to release constituent carbohydrates from biomass feed-stocks and during fermentation, exposure of the organisms to stressful conditions. In addition, for lignocellulosic bioethanol production, conversion of both pentose and hexose sugars is a pre-requisite for fermentative organisms for efficient and complete conversion. All these factors are important to maximise industrial efficiency, productivity and profit margins in order to make second-generation bioethanol an economically viable alternative to fossil fuels for future transport needs.ResultsThe aim of the current study was to assess Saccharomyces yeasts for their capacity to tolerate osmotic, temperature and ethanol stresses and inhibitors that might typically be released during steam explosion of wheat straw. Phenotypic microarray analysis was used to measure tolerance as a function of growth and metabolic activity. Saccharomyces strains analysed in this study displayed natural variation to each stress condition common in bioethanol fermentations. In addition, many strains displayed tolerance to more than one stress, such as inhibitor tolerance combined with fermentation stresses.ConclusionsOur results suggest that this study could identify a potential candidate strain or strains for efficient second generation bioethanol production. Knowledge of the Saccharomyces spp. strains grown in these conditions will aid the development of breeding programmes in order to generate more efficient strains for industrial fermentations.
Highlights
During industrial fermentation of lignocellulose residues to produce bioethanol, microorganisms are exposed to a number of factors that influence productivity
These included the utilisation of hexose and pentose sugars, resistance to conditions within bioreactors, such as osmotic, ethanol and temperature stress and resistance to phenolic and aromatic inhibitory compounds formed during the steam explosion of lignocellulosic waste
Utilisation of hexose and pentose sugars by Saccharomyces spp. strains Hydrolysates derived from Lignocellulosic material (LCM) contain hexose and pentose sugars, [33], metabolic output on glucose, xylose and arabinose was measured
Summary
During industrial fermentation of lignocellulose residues to produce bioethanol, microorganisms are exposed to a number of factors that influence productivity. For lignocellulosic bioethanol production, conversion of both pentose and hexose sugars is a pre-requisite for fermentative organisms for efficient and complete conversion. All these factors are important to maximise industrial efficiency, productivity and profit margins in order to make second-generation bioethanol an economically viable alternative to fossil fuels for future transport needs. S. cerevisiae strains are unable to efficiently utilise pentose sugars [7], despite containing a xylose utilisation pathway [8] and an arabinose metabolic pathway [9]. Five clean lineage strains (West African, Wine European, Sake, North American and Malaysian) of S. cerevisiae that are representative of specific genomic clades have been identified [22] and engineered to enable genetic tractability [23,24,25]
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