Characterization of bacteriocins produced by strains from traditional Bulgarian dairy products.

A result of extensive screening of over 300 strains from the Collection of ELBY Bulgaricum, PLC, thirty six strains were selected as producers of bacteriocins, active closely related lactic acid bacterial species and some food spoilage bacteria. The selected strains belong to L. helveticus, L. bulgaricus and S. thermophilus, which are rare bacteriocin producers. Nineteen nonidentified producers were characterized by molecular taxonomic approaches--M13 fingerprinting, repetitive PCR, ribotyping and hybridization with species-specific probes, which allowed to affiliate them to the species L. delbrueckii. Several strains were found to harbour plasmids of different size. The estimated activity against food borne pathogens makes the isolated substances perspective as safe food preservatives and the producing strains could be used as components of starters with improved quality.

Comparative genome analysis of Bacillus sphaericus by ribotyping, M13 hybridization, and M13 polymerase chain reaction fingerprinting.

A comparative genome analysis of 15 strains representing the five homology groups of the highly heterogeneous species Bacillus sphaericus was performed by M13 hybridization fingerprinting, M13 polymerase chain reaction fingerprinting, and ribotyping with the whole rrn operon. The computer cluster analyses of the polymorphic patterns, presented in dendrograms, showed that these methods allow the differentiation of the individual strains and some homology groups. Our results confirm the close genetic relatedness of the mosquito pathogenic strains of group IIA and support the idea for differentiation of a separate species. At the same time, we present additional proof of the significant genetic heterogeneity of B. sphaericus and the necessity of reconsideration of its present classification.