Comparative analysis of the genes encoding 23S-5S rRNA intergenic spacer regions of Lactobacillus casei-related strains

In this study, investigations into the 23S-5S rRNA intergenic spacer region s (ISRs) of the Lactobacillus casei group were performed. A 1.6 kb fragment , from Lactobacillus paracasei strain ATCC 27092, containing part of the 5S rRNA gene (60 bp), the 5S-23S spacer region (198 bp) and part of the 23S r RNA gene (1295 bp) was cloned and sequenced (GenBank no. AF098107). This fr agment was used as a probe to determine the rRNA restriction fragment lengt h polymorphism (RFLP) patterns of nine strains belonging to the Lactobacill us casei group, along with four other non-Lactobacillus casei lactobacilli species. A pair of PCR primers, 23-FI and 5-Ru, was designed and used for P CR amplification of the 23S-5S rRNA ISRs of these strains. The ISR length a nd sequence polymorphisms provided additional information for the taxonomic study of the Lactobacillus casei group. The spacer-length polymorphism of Lactobacillus rhamnosus was distinct from those of the other strains and th is observation is consistent with the classification of Lactobacillus rhamn osus proposed by Mori et al. For all Lactobacillus casei and Lactobacillus paracasei strains, two major bands (approx. 250 and 170 bp in size) were ob tained except in the case of Lactobacillus paracasei subsp. tolerans strain NCIMB 9709(T), which yielded only one amplified product (250 bp). The sequ encing data of the PCR products of seven well-characterized Lactobacillus c asei and Lactobacillus paracasei strains revealed the presence of a 76/80 b p insertion/deletion with some random, single-base substitutions between th e longer and shorter spacers for each respective strain. A few base variati ons were also detected within different strains in this group although the overall sequence similarity was very high (95.9-99.5%). The rRNA RFLP and t he spacer sequence of Lactobacillus casei type strain ATCC 393(T) exhibited unique identities in this cluster. On the other hand, Lactobacillus casei strain ATCC 334 showed a high level of similarity with the other Lactobacil lus casei strains tested. These observations lend some support to the reque st for the reassignment of strain ATCC 334 as the neotype of Lactobacillus casei subsp. casei in place of strain ATCC 393T.