title: UDP-galactose 4-epimerase: a key enzyme in exopolysaccharide formation by Lactobacillus casei CRL 87 in controlled pH batch cultures.
abstract: OBJECTIVE
  To evaluate the relationship between exopolysaccharide (EPS) production and the sugar nucleotide biosynthetic enzymes in Lactobacillus casei CRL 87 under optimum growth conditions for polymer formation: controlled pH on galactose or glucose. Studies with an EPS mutant were carried out to determine the key enzymes in EPS synthesis under the above culture conditions.
  
  
  RESULTS
  EPS concentration was estimated by the phenol/sulphuric acid method, while the activities of the biosynthetic enzymes were determined spectrophotometrically by measuring the formation or disappearance of NAD(P)H at 340 nm. An environmental pH of 5.0, using galactose as carbon source, markedly improved not only polymer production and yield but also, cell growth and lactic acid production. Analysis of the activities of the EPS precursor-forming enzymes revealed that polysaccharide synthesis was correlated with uridine-diphosphate (UDP)-glucose pyrophosphorylase and UDP-galactose 4-epimerase under these growth conditions.
  
  
  CONCLUSIONS
  EPS synthesis by Lact. casei CRL 87 was considerably improved at a controlled pH of 5.0 with galactose as carbon source, and was correlated with the activity of UDP-glucose pyrophosphorylase and UDP-galactose 4-epimerase. The results obtained with the wild-type and EPS- strains suggest that UDP-galactose 4-epimerase plays an essential role in EPS formation.
  
  
  CONCLUSIONS
  Unravelling the key enzymes involved in EPS biosynthesis under optimum culture conditions for polymer production provides important information for the design of strategies, via genetic engineering, to enhance polysaccharide formation.
authors.affiliation: Centro de Referencia para Lactobacilos (CERELA)-CONICET, Tucumán, Argentina. fmozzi@cerela.org.ar
authors.forename: F
authors.initials: F
authors.lastname: Mozzi
authors.forename: G
authors.initials: G
authors.lastname: Savoy de Giori
authors.forename: G
authors.initials: G
authors.lastname: Font de Valdez
mesh_terms: D003470:Culture Media; D005285:Fermentation; D005690:Galactose / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007780:Lacticaseibacillus casei / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D009154:Mutation / Q000235:genetics; D009711:Nucleotides / Q000096:biosynthesis; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D014534:UDPglucose 4-Epimerase / Q000378:metabolism*; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase / Q000378:metabolism
chemical_list: D003470:Culture Media; D009711:Nucleotides; D011135:Polysaccharides, Bacterial; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase; D014534:UDPglucose 4-Epimerase; D005947:Glucose; D005690:Galactose