Applied and Environmental Microbiology, August 2000, p. 3519-3527, Vol. 66, No. 8
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
-Phosphoglucomutase, UDP-Galactose 4-Epimerase, and UDP-Glucose
Pyrophosphorylase with Exopolysaccharide Biosynthesis by
Streptococcus thermophilus LY03
Research Group of Industrial Microbiology, Fermentation Technology and Downstream Processing, Department of Applied Biological Sciences, Vrije Universiteit Brussel, B-1050 Brussels, Belgium
Received 18 February 2000/Accepted 30 May 2000
The effects of different carbohydrates or mixtures of carbohydrates
as substrates on bacterial growth and exopolysaccharide (EPS) production were studied for the yoghurt starter culture Streptococcus thermophilus LY03. This strain produces two
heteropolysaccharides with the same monomeric composition (galactose
and glucose in the ratio 4:1) but with different molecular masses.
Lactose and glucose were fermented by S. thermophilus
LY03 only when they were used as sole energy and carbohydrate sources.
Fructose was also fermented when it was applied in combination with
lactose or glucose. Both the amount of EPS produced and the
carbohydrate source consumption rates were clearly influenced by the
type of energy and carbohydrate source used, while the EPS monomeric
composition remained constant (galactose-glucose, 4:1) under all
circumstances. A combination of lactose and glucose resulted in the
largest amounts of EPS. Measurements of the activities of enzymes
involved in EPS biosynthesis, and of those involved in sugar nucleotide
biosynthesis and the Embden-Meyerhof-Parnas pathway, demonstrated that
the levels of activity of
-phosphoglucomutase, UDP-galactose
4-epimerase, and UDP-glucose pyrophosphorylase are highly correlated
with the amount of EPS produced. Furthermore, a weaker relationship or no relationship between the amounts of EPS and the enzymes involved in
either the rhamnose nucleotide synthetic branch of the EPS biosynthesis
or the pathway leading to glycolysis was observed for S. thermophilus LY03.
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