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Appl. Environ. Microbiol., 01 1997, 128-132, Vol 63, No. 1
S Bjorkqvist, R Ansell, L Adler and G Liden
Mutants of Saccharomyces cerevisiae, in which one or both of the genes
encoding the two isoforms of NAD-dependent glycerol-3-phosphate
dehydrogenase had been deleted, were studied in aerobic batch cultures and
in aerobic-anaerobic step change experiments. The respirofermentative
growth rates under aerobic conditions with semisynthetic medium (20 g of
glucose per liter) of two single mutants, gpd1 delta and gpd2 delta, and
the parental strain (mu = 0.5 h-1) were almost identical, whereas the
growth rate of a double mutant, gpd1 delta gpd2 delta, was approximately
half that of the parental strain. Upon a step change from aerobic to
anaerobic conditions in the exponential growth phase, the specific carbon
dioxide evolution rates (CER) of the wild-type strain and the gpd1 delta
strain were almost unchanged. The gpd2 delta mutant showed an immediate,
large (> 50%) decrease in CER upon a change to anaerobic conditions.
However, after about 45 min the CER increased again, although not to the
same level as under aerobic conditions. The gpd1 delta gpd2 delta mutant
showed a drastic fermentation rate decrease upon a transition to anaerobic
conditions. However, the CER values increased to and even exceeded the
aerobic levels after the addition of acetoin. High-pressure liquid
chromatographic analyses demonstrated that the added acetoin served as an
acceptor of reducing equivalents by being reduced to butanediol. The
results clearly show the necessity of glycerol formation as a redox sink
for S. cerevisiae under anaerobic conditions.
Copyright © 1997, American Society for Microbiology
Physiological response to anaerobicity of glycerol-3-phosphate dehydrogenase mutants of Saccharomyces cerevisiae
Department of Chemical Reaction Engineering, Chalmers University of Technology, Goteborg, Sweden.
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