title: Sequence heterogeneity in the lacSZ operon of Streptococcus thermophilus and its use in PCR systems for strain differentiation.
abstract: Sequences of the lacSZ operon of 29 Streptococcus thermophilus strains from different dairy products were determined. Differences in sequence among the strains were detected within LacS more often than in the LacZ gene. The sequences were aligned and compared and it was possible to gather the strains into three groups of similarity on the basis of the LacS gene sequence. The dairy environment of origin did not seem to be related to the lacSZ operon sequence and thus to the similarity shown. Nucleotide variability was investigated and a total of 139 nucleotide changes were found in the LacS gene while 40 nucleotide changes were found in the sequences of the LacZ gene. Moreover, the influence of the nucleotide changes on the amino acid sequence of the LacS transporter and of the beta-galactosidase enzyme were discussed. Sequence variability within the region upstream from the LacS gene was used to develop group-specific PCR systems capable of distinguishing S. thermophilus at the strain level. A strain-specific primer set was designed allowing the specific detection of 11 out of 29 strains of S. thermophilus. Moreover, LacS-PCR-SSCP analysis of the 29 strains provided 2 different profiles, whereas 4 strain-specific profiles were detected by LacS-PCR-DGGE, indicating the potential to use these techniques for profiling and monitoring population of strains of S. thermophilus in food products. The results are discussed with reference to the potential of these PCR methods for ascertaining strain dominance and starter fitness in dairy processes.
authors.affiliation: Dipartimento di Scienza degli Alimenti, Sezione di Microbiologia Agraria, Alimentare e Ambientale e di Igiene, Stazione di Microbiologia Industriale, Università degli Studi di Napoli Federico II, via Università 100, 80055 Portici, Italy.
authors.forename: Danilo
authors.initials: D
authors.lastname: Ercolini
authors.forename: Vincenzina
authors.initials: V
authors.lastname: Fusco
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Blaiotta
authors.forename: Salvatore
authors.initials: S
authors.lastname: Coppola
mesh_terms: D015373:Bacterial Typing Techniques; D001483:Base Sequence; D004591:Electrophoresis, Polyacrylamide Gel / Q000379:methods; D014644:Genetic Variation; D007763:Lac Operon / Q000235:genetics*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction / Q000379:methods*; D018807:Polymorphism, Single-Stranded Conformational; D017422:Sequence Analysis, DNA; D048249:Streptococcus thermophilus / Q000145:classification* / Q000235:genetics