Affiliation:
1. Section of Molecular Microbiology, BioCentrum, Technical University of Denmark, DK-2800 Lyngby, Denmark
Abstract
ABSTRACT
Two mutant strains of
Lactococcus lactis
in which the promoter of the
las
operon, harboring
pfk, pyk
, and
ldh
, were replaced by synthetic promoters were constructed. These
las
mutants had an approximately twofold decrease in the activity of phosphofructokinase, whereas the activities of pyruvate kinase and lactate dehydrogenase remained closer to the wild-type level. In defined medium supplemented with glucose, the growth rate of the mutants was reduced to 57 to 70% of wild-type levels and the glycolytic flux was reduced to 62 to 76% of wild-type levels. In complex medium growth was even further reduced. Surprisingly, the mutants still showed homolactic fermentation, which indicated that the limitation was different from standard glucose-limited conditions. One explanation could be that the reduced activity of phosphofructokinase resulted in the accumulation of sugar-phosphates. Indeed, when one of the mutants was starved for glucose in glucose-limited chemostat, the growth rate could gradually be increased to 195% of the growth rate observed in glucose-saturated batch culture, suggesting that phosphofructokinase does affect the concentration of upstream metabolites. The pools of glucose-6-phosphate and fructose-6-phosphate were subsequently found to be increased two- to fourfold in the
las
mutants, which indicates that phosphofructokinase exerts strong control over the concentration of these metabolites.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
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2000
Department of Microbiology
Technical University of DenmarkLyngby Denmark
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