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Enhanced Exopolysaccharide Production by Metabolic Engineering of Streptococcus thermophilus.

In English

Författare

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.

Publiceringsår

2002

Språk

Engelska

Sidor

784-790

Publikation/Tidskrift/Serie

Applied and Environmental Microbiology

Volym

68

Issue

2

Dokumenttyp

Artikel i tidskrift

Förlag

American Society for Microbiology

Ämne

  • Industrial Biotechnology

Nyckelord

  • 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/Övrigt

  • ISSN: 0099-2240