Genome comparison of Lactococcus strains by pulsed-field gel electrophoresis

The two restriction enzymes SmaI and ApaI were found to produce distributions of DNA fragments useful for genome analysis of some lactic acid bacteria (Lactococcus lactis and Streptococcus salivarius subsp. thermophilus) by pulsed-field gel electrophoresis. The genome size was estimated to be 1750 to 2500 kb depending on the species. Each strain displayed unique restriction patterns; nevertheless, the percentage of the comigrating fragments of two isogenic or closely related strains was about 80% and fell to 20-40% when the patterns of two non-related strains of the same species or two strains belonging to different species were compared.