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Applied and Environmental Microbiology, September 2001, p. 3976-3984, Vol. 67, No. 9
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.9.3976-3984.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

UDP-N-Acetylglucosamine 4-Epimerase Activity Indicates the Presence of N-Acetylgalactosamine in Exopolysaccharides of Streptococcus thermophilus Strains

Bart Degeest,1 Frederik Vaningelgem,1 Andrew P. Laws,2 and Luc De Vuyst1,*

Research Group of Industrial Microbiology, Fermentation Technology and Downstream Processing (IMDO), Department of Applied Biological Sciences, Vrije Universiteit Brussel, B-1050 Brussels, Belgium,1 and School of Applied Sciences, University of Huddersfield, HD1 3DH Huddersfield, United Kingdom2

Received 16 February 2001/Accepted 15 June 2001

The monomer composition of the exopolysaccharides (EPS) produced by Streptococcus thermophilus LY03 and S. thermophilus Sfi20 were evaluated by high-pressure liquid chromatography with amperometric detection and nuclear magnetic resonance spectroscopy. Both strains produced the same EPS composed of galactose, glucose, and N-acetylgalactosamine. Further, it was demonstrated that the activity of the precursor-producing enzyme UDP-N-acetylglucosamine 4-epimerase, converting UDP-N-acetylglucosamine into UDP-N-acetylgalactosamine, is responsible for the presence of N-acetylgalactosamine in the EPS repeating units of both strains. The activity of UDP-N-acetylglucosamine 4-epimerase was higher in both S. thermophilus strains than in a non-EPS-producing control strain. However, the level of this activity was not correlated with EPS yields, a result independent of the carbohydrate source applied in the fermentation process. On the other hand, both the amounts of EPS and the carbohydrate consumption rates were influenced by the type of carbohydrate source used during S. thermophilus Sfi20 fermentations. A correlation between activities of the enzymes alpha -phosphoglucomutase, UDP-glucose pyrophosphorylase, and UDP-galactose 4-epimerase and EPS yields was seen. These experiments confirm earlier observed results for S. thermophilus LY03, although S. thermophilus Sfi20 preferentially consumed glucose for EPS production instead of lactose in contrast to the former strain.

* Corresponding author. Mailing address: Research Group of Industrial Microbiology, Fermentation Technology and Downstream Processing (IMDO), Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussels, Belgium. Phone: 32-2-6293245. Fax: 32-2-6292720. E-mail: ldvuyst{at}vub.ac.be.

Applied and Environmental Microbiology, September 2001, p. 3976-3984, Vol. 67, No. 9
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.9.3976-3984.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


This article has been cited by other articles:

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