Lactobacillus helveticus: Strain typing and genome size estimation by pulsed field gel electrophoresis

Genomic DNAs of 22 strains of Lactobacillus helveticus of various geographical origins were analyzed by pulsed-field gel electrophoresis. Two endonucleases, SmaI and SgrAI, of the 19 tested produced DNA fragments useful for strain comparison. With the endonuclease SmaI, a characteristic restriction pattern was identified for 18 of the 22 strains. The percentage of similarity (Dice coefficient) between the profiles varied between 26% and 100%, and clustering was accomplished by using the unweighted pair group method with arithmetic averages (UPGMA). For the strains showing identical profiles, the high genomic similarity was confirmed when the endonuclease SgrAI was used instead of SmaI. From summation of SmaI and SgrAI fragments from three L. helveticus strains (CNRZ 241, CNRZ 303, and CIP 57.15), the genomic length was estimated at ca. 1.85-2.0 Mb.