V. ALEKSANDROVA, D. ISHLIMOVA and Z. URSHEV
LB BULGARICUM PLC – R&D Center, 12A Malashevska str., BG – 1202 Sofia, Bulgaria
Aleksandrova, V., D. Ishlimova and Z. Urshev, 2013. Classification of Lactobacillus delbrueckii ssp. bulgaricus phage Gb1 into group “b” Lactobacillus delbrueckii bacteriophages based on its partial genome sequencing. Bulg. J. Agric. Sci., Supplement 2, 19: 90–93
The modular evolution of phage genomes makes their classification extremely difficult. Still in dairy industry, the identification of the phage species that disturbs the fermentation process is of crucial importance in the selection of a strategy to avoid or eliminate phage infections. Phages attacking Lactobacillus delbrueckii are currently divided into four groups assigned as “a”, “b”, “c” and “d” which have substantial differences in their virion morphology and DNA homology. Lactobacillus delbrueckii ssp. bulgaricus phage Gb1 was isolated in 2005 from yoghurt production. Restriction fragments of phage Gb1 DNA were cloned into pIL253 in Lactococcus lctis IL1403 and PCR amplified with vector-specific primers. The resulting amplicons were sequenced and identities with existing sequence databases were searched. All of the obtained sequences showed homology only to regions within the genome of phages LL-Ku and c5 with levels of nucleotide identity of 80-99%. No significant sequence matches were found with other L. delbrueckii phages. The sequenced fragments from the genome of phage Gb1 were homologous to key genes in phages LL-Ku and c5 encoding a major head protein, the tape-measure protein, tail proteins, the single strand binding protein and a diesterase. As phages LL-Ku and c5 are typical representatives of group “b” L. delbrueckii bacteriophages that do not share DNA homology with L. delbrueckii phages from other groups we could classifyphage Gb1 into group “b” L. delbrueckii phages. This is the first report of a bacteriophage from this group isolated in Bulgaria. Further studies of phage Gb1 will facilitate the work on the selection of phage resistant starters and prevention of phage infections in yoghurt production.