Studies on the large subunit rRNA genes and their flanking regions of leuconostocs

The 16S-23S (spacer-1) and 23S-5S (spacer-2) rRNA intergenic spacer regions of Leucortostoc lactis, Leuconostoc mesenteroides, Leuconostoc mesenteroid es subsp. dextranicum, and Leuconostoc mesenteroides subsp. cremoris were a mplified by polymerase chain reactions and sequenced. The 23S rRNA genes of Lenconostoc lactis, Leuconostoc mesenteroides, and Leuconostoc mesenteroid es subsp. dextranicum were also sequenced. The RNase III-like and RNase E p rocessing sites, as well as putative antitermination signals, were identifi ed within the spacer regions. A single tRNA(Ala) gene without the 3"-termin al CCA sequence was found in spacer-1 regions. Secondary structure models a re proposed showing interactions between the two spacer regions of leuconos tocs. For all strains studied, spacer-1 and spacer-2 were highly conserved and therefore could not be directly used for strain typing. Sequence inform ation on 23S rRNA genes from Leuconostoc species allowed the determination of regions that can be used as targets for diagnostic probes and amplificat ion primers. Secondary structures of variable helical elements of leuconost ocs 23S rRNA were constructed and their primary structures were compared wi th those of several Grampositive bacteria with low G+C contents. Comparativ e analysis revealed that restriction analysis of 23S rRNA variable regions appeared to be sufficient for the search for species-specific signatures. O ur experimental observations revealed that one form of the rRNA operons was present in leuconostocs. We have also demonstrated the direct Linkage betw een the three species of rRNA genes, which are organized as follows: 5'-16S rRNA - spacer-1 - tRNAAla - 23S rRNA spacer-2 - 5S rRNA-3.