title: Yoghurt fermentation at elevated temperatures by strains of Streptococcus thermophilus expressing a small heat-shock protein: application of a two-plasmid system for constructing food-grade strains of Streptococcus thermophilus.
abstract: Streptococcus thermophilus S4 expressing a small heat-shock protein from the plasmid pSt04-encoded copy of shsp, is able to carry out fermentation at elevated temperature, i.e., at 50 degrees C. In yoghurt culture together with Lactobacillus delbrueckii subsp. bulgaricus, fermentation at elevated temperature results in a mild yoghurt with low post-acidification and improved stability of the starter bacteria during storage at 4 degrees C. To transfer pSt04 into commercial S. thermophilus yoghurt starter strains, a two-plasmid system was constructed. A helper plasmid providing a selectable antibiotic marker, but relying on the repA gene of pSt04, was transformed together with pSt04. After isolation of transformants, the helper plasmid was readily lost upon incubation of transformants in antibiotic-free medium, thus yielding food-grade strains carrying pSt04 only. Successful application of the system was demonstrated.
authors.affiliation: Institute for Microbiology, Federal Research Center for Nutrition and Food, Kiel, Germany.
authors.forename: Hassan A
authors.initials: HA
authors.lastname: El Demerdash
authors.forename: Julian
authors.initials: J
authors.lastname: Oxmann
authors.forename: Knut J
authors.initials: KJ
authors.lastname: Heller
authors.forename: Arnold
authors.initials: A
authors.lastname: Geis
mesh_terms: D018929:Cell Culture Techniques / Q000379:methods; D018920:Coculture Techniques / Q000379:methods; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D005285:Fermentation; D005511:Food Handling / Q000379:methods*; D024861:Genetic Enhancement / Q000379:methods; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D007778:Lactobacillus / Q000378:metabolism*; D010957:Plasmids / Q000235:genetics; D015202:Protein Engineering / Q000379:methods*; D013045:Species Specificity; D048249:Streptococcus thermophilus / Q000235:genetics / Q000378:metabolism*; D013696:Temperature; D015014:Yogurt / Q000032:analysis / Q000382:microbiology*
chemical_list: D006360:Heat-Shock Proteins