16S-23S AND 23S-5S INTERGENIC SPACER REGIONS OF LACTOBACILLI - NUCLEOTIDE-SEQUENCE, SECONDARY STRUCTURE AND COMPARATIVE-ANALYSIS

Lactobacilli have been used as industrial starters for a long time, bu t in several cases their identification was, and still is, neither eas y nor reliable. The aim of the present work was to examine whether the intergenic spacer regions could be of value in the identification of Lactobacillus species. For that purpose, the polymerase chain reaction (PCR) was used to amplify 16S-23S and 23S-5S spacer regions of Lactob acillus (L.) acidophilus, L. delbrueckii subsp. bulgaricus, L.casei, L . helveticus and L. curvatus. The FOR products were directly sequenced , and two forms of ribosomal RNA (rm) operons were identified in each species studied: one with tandem tRNA(lle)/tRNA(Ala) genes and the oth er one without tRNA genes. Our study revealed that the rm operons of L actobacillus species studied comprise the genes of 16S, 23S and 5S rRN A, in that order. Only the tRNA genes and the rRNA processing stems ar e highly conserved in spacer regions of lactobacilli. The divergence b etween the lactobacilli spacer region sequences arises from insertions and deletions of short sequences. These sequences could be interestin g candidates for the development of species-specific probes. Theoretic al RNA/RNA secondary structure models of the interaction between the t wo spacer region sequences were constructed. In conclusion, the two sp acer region sequences may prove to be a useful alternative to 16S and 23S rDNA sequencing for designing species-specific probes and for esta blishing phylogenetic relationships between closely related species su ch as L. curvatus and L. casei or L. acidophilus and L. helveticus.