Phage-related DNA polymorphism in dairy and probiotic Lactobacillus

Various DNA-based methods are presently being applied For identification of industrial bacterial cultures including dairy starter and probiotic strain s of Lactobacillus. The success of strain-specific identification depends o n the power of the DNA-based methods to reveal intraspecies DNA polymorphis m. This study reveals that all eleven arbitrarily chosen Lactobacillus rham nosus starter, laboratory and probiotic strains contain Lb. rhamnosus phage Lc-Nu related nucleotide sequences. One of these highly homologous regions in the genome of phage Lc-Nu was the 2.4 kb HindIII fragment, which has be en sequenced. Nucleotide sequence analysis suggested that one side of the 2 .4 kb HindIII fragment encodes a phage Lc-Nu helicase and accordingly repre sents an early gene region of phage Lc-Nu genome. Five forward and five rev erse primers were derived from the nucleotide sequence of the 2.4 kb HindII I fragment of phage Lc-Nu DNA for PCR-based identification of the eleven Lb . rhamnosus strains included in this study. Six different types of PCR prod uct patterns were obtained. Among the patterns three were unique to particu lar Lb, rhamnosus strains. The results suggest that phage-related DNA seque nces are, surprisingly, distributed widely among the Lb. rhamnosus strains, and that these sequences could also be a source of DNA polymorphism to app ly for DNA-based identification of bacterial strains. Phage Lc-Nu related D NA homology was also found in the chromosome of Lb. casei, the species clos ely related to LB. rhamnosus. (C) 2000 Elsevier Science Ltd. All rights res erved.