Anaerobic glycerol production by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis> strains under hyperosmotic stress |
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Authors: | Tobias Modig Katarina Granath Lennart Adler Gunnar Lidén |
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Institution: | Department of Chemical Engineering, Lund University, Box 124, 221 00, Lund, Sweden. tobias.modig@chemeng.lth.se |
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Abstract: | Glycerol formation is vital for reoxidation of nicotinamide adenine dinucleotide (reduced form; NADH) under anaerobic conditions
and for the hyperosmotic stress response in the yeast Saccharomyces cerevisiae. However, relatively few studies have been made on hyperosmotic stress under anaerobic conditions. To study the combined
effect of salt stress and anaerobic conditions, industrial and laboratory strains of S. cerevisiae were grown anaerobically on glucose in batch-cultures containing 40 g/l NaCl. The time needed for complete glucose conversion
increased considerably, and the specific growth rates decreased by 80–90% when the cells were subjected to the hyperosmotic
conditions. This was accompanied by an increased yield of glycerol and other by-products and reduced biomass yield in all
strains. The slowest fermenting strain doubled its glycerol yield (from 0.072 to 0.148 g/g glucose) and a nearly fivefold
increase in acetate formation was seen. In more tolerant strains, a lower increase was seen in the glycerol and in the acetate,
succinate and pyruvate yields. Additionally, the NADH-producing pathway from acetaldehyde to acetate was analysed by overexpressing
the stress-induced gene ALD3. However, this had no or very marginal effect on the acetate and glycerol yields. In the control experiments, the production
of NADH from known sources well matched the glycerol formation. This was not the case for the salt stress experiments in which
the production of NADH from known sources was insufficient to explain the formed glycerol. |
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Keywords: | ALD3 Glycerol Osmotic stress Saccharomyces cerevisiae |
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