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Enhanced Exopolysaccharide Production by Metabolic Engineering of Streptococcus thermophilus.

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Author

Summary, in English

It is possible that the low levels of production of exopolysaccharides (EPSs) by lactic acid bacteria could be improved by altering the levels of enzymes in the central metabolism that influence the production of precursor nucleotide sugars. To test this hypothesis, we identified and cloned the galU gene, which codes for UDP glucose pyrophosphorylase (GalU) in Streptococcus thermophilus LY03. Homologous overexpression of the gene led to a 10-fold increase in GalU activity but did not have any effect on the EPS yield when lactose was the carbon source. However, when galU was overexpressed in combination with pgmA, which encodes phosphoglucomutase (PGM), the EPS yield increased from 0.17 to 0.31 g/mol of carbon from lactose. A galactose-fermenting LY03 mutant (Gal(+)) with increased activities of the Leloir enzymes was also found to have a higher EPS yield (0.24 g/mol of carbon) than the parent strain. The EPS yield was further improved to 0.27 g/mol of carbon by overexpressing galU in this strain. However, the highest EPS yield, 0.36 g/mol of carbon, was obtained when pgmA was knocked out in the Gal(+) strain. Measurements of the levels of intracellular metabolites in the cultures revealed that the Gal(+) strains had considerably higher glucose 1-phosphate levels than the other strains, and the strain lacking PGM activity had threefold-higher levels of glucose 1-phosphate than the other Gal(+) strains. These results show that it is possible to increase EPS production by altering the levels of enzymes in the central carbohydrate metabolism.

Publishing year

2002

Language

English

Pages

784-790

Publication/Series

Applied and Environmental Microbiology

Volume

68

Issue

2

Document type

Journal article

Publisher

American Society for Microbiology

Topic

  • Industrial Biotechnology

Keywords

  • Genetic Engineering/*methods
  • Molecular Sequence Data
  • Phosphoglucomutase/genetics/metabolism
  • UTP-Glucose-1-Phosphate Uridylyltransferase/*genetics/*metabolism
  • Non-U.S. Gov't
  • Support
  • Streptococcus/*enzymology/genetics/growth & development
  • Polysaccharides
  • Bacterial/*biosynthesis
  • Galactose/metabolism
  • Molecular
  • Culture Media
  • Cloning
  • Base Sequence

Status

Published

ISBN/ISSN/Other

  • ISSN: 0099-2240