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Applied and Environmental Microbiology, January 2001, p. 33-41, Vol. 67, No. 1
Instituto de Tecnologia Química e
Biológica/Universidade Nova de Lisboa and Instituto de Biologia
Experimental e Tecnológica, 2780-156 Oeiras,
Portugal,1 and NIZO Food Research and
Wageningen Centre for Food Sciences, 6710 BA Ede, The
Netherlands2
Received 15 May 2000/Accepted 10 October 2000
The relationships between glucose metabolism and exopolysaccharide
(EPS) production in a Lactococcus lactis strain containing the EPS gene cluster (Eps+) and in nonproducer strain
MG5267 (Eps
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.1.33-41.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Relationship between Glycolysis and
Exopolysaccharide Biosynthesis in Lactococcus
lactis
) were characterized. The concentrations of
relevant phosphorylated intermediates in EPS and cell wall biosynthetic
pathways or glycolysis were determined by 31P nuclear
magnetic resonance. The concentrations of two EPS precursors, UDP-glucose and UDP-galactose, were significantly lower in the Eps+ strain than in the Eps
strain. The
precursors of the peptidoglycan pathway,
UDP-N-acetylglucosamine and
UDP-N-acetylmuramoyl-pentapeptide, were the major UDP-sugar derivatives detected in the two strains examined, but the concentration of the latter was greater in the Eps+ strain, indicating
that there is competition between EPS synthesis and cell growth. An
intermediate in biosynthesis of histidine and nucleotides,
5-phosphorylribose 1-pyrophosphate, accumulated at concentrations in
the millimolar range, showing that the pentose phosphate pathway was
operating. Fructose 1,6-bisphosphate and glucose 6-phosphate were the
prominent glycolytic intermediates during exponential growth of both
strains, whereas in the stationary phase the main metabolites were
3-phosphoglyceric acid, 2-phosphoglyceric acid, and
phosphoenolpyruvate. The activities of relevant enzymes, such as
phosphoglucose isomerase,
-phosphoglucomutase, and UDP-glucose pyrophosphorylase, were identical in the two strains. 13C
enrichment on the sugar moieties of pure EPS showed that glucose 6-phosphate is the key metabolite at the branch point between glycolysis and EPS biosynthesis and ruled out involvement of the triose
phosphate pool. This study provided clues for ways to enhance EPS
production by genetic manipulation.
*
Corresponding author. Mailing address: Instituto de
Tecnologia Química e Biológica/Universidade Nova de
Lisboa, Rua da Quinta Grande, 6, Apt. 127, 2780-156 Oeiras, Portugal.
Phone: 351-21-4469828. Fax: 351-21-4428766. E-mail:
santos{at}itqb.unl.pt.
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