Türkiye kökenli Lactococcus lactis suşlarının kromozomal farklılıklarının tanımlanması
In this study, 30 Lactococcus lactis strains originating from raw milk isolated in Turkey, which are defined by phenotypic tests at the strain level, were characterized by molecular techniques. A few typing techniques were estimated to determine the genetic diversity of strains. First of all, plasmid profiling was used in order to both identify the isolates at the strain level and determine the similarities between the strains. It has been identified that all strains have one or more plasmid. It was determined that all strains, which are considered as L. lactis subsp. lactis, L. lactis subsp. cremoris and L. lactis subsp. lactis biovar diacetylactis, showed different plasmid profiles. Strains from one cluster which shows 55% similarity when plasmid profiles were compared. Pulsed-field gel electrophoresis (PFGE) analysis of complete genomes digested with SmaI, ApaI and I-CeuI restriction endonucleases proved that all strains were similar out of four isolates, which showed different PFGE profiles from the others. Results showed a high degree of heterogeneity among determined with PFGE twenty six L. lactis strains. Taking account of the chromosomal differences between strains after SmaI restriction digestion process, 10 of strains were clustered at a similarity level of about 75% with L. lactis subsp. lactis ATCC 7962 and IL1403 which are used as reference strain, and 3 of strains were clustered at a same similarity level with L. lactis subsp. cremoris MG1614 which are used as reference strain. On the other hand, 13 strains, which are mostly L. lactis subsp. lactis biovar diacetylactis, were clustered at a similarity level of 65%. It is known that L. lactis strains have 6 rRNA operons. I-Ceul restriction endonuclease digests from 23S rDNA operon regions, which are well preserved in evolutionary processes and produces 6 macrorestriction patterns for L. lactis strains. The strains, which have differences between numbers of operons, confirmed by PCR using specific primers designed for conserved 16S rDNA regions. Results of 16S rDNA sequencing showed that 4 of strains are identified incorrect, 3 of strains are Streptococcus bovis and 1 of the strains is Enterococcus durans.