The 165-235 and 235-55 rRNA spacer DNA regions (spacer regions 1 and 2, respectively) from Enterococcus faecalis, Enterococcus faecium, Enterncoccus hirae, Enterococcus durans and Enterncoccus mundtii were amplified by PCR. Their nucleotide sequences were established and a secondary structure model showing the interaction between the two spacer regions was built. Whereas lactococci and Streptococcus sensu stricto are characterized by a single type of spacer region 1 , the enterococci show a high degree of variability in this region; thus the spacer regions 1 with and without tRNAAia were characterized. However, as shown for lactococci and Streptococcus sensu stricto, the tRNAAia gene does not encode the 3'4erminal CCA trinucleotide. A putative antitermination signal is found downstream from the tRNAAia gene. Based on comparison with Lactococcus lactis and Streptococcus thermophilus, a doublestranded processing stem is proposed. In €. hirae, one of the three different types of spacer region 1 contains no tRNAAia, but displays a 107 nt insertion that forms a long stem-loop structure. A similar insertion (1 15 nt in length) was found in E. faecium and base compensatory mutations preserve the ability to form the long stem-loop structure. Such insertions may correspond to mobile intervening sequences, as found in the 235 rRNA coding sequences of some Gram-negative bacteria. The spacer regions 1 and 2 from the three subgroups of streptococci were compared, and except for the tRNAAia gene and the double-stranded processing sites, little similarity was found, which opens large possibilities for future development of DNA-based typing methods.
The 16S-23S intergenic spacer region (spacer region 1) of Streptococcus salivarius, S. thermophilus, and Lactococcus lactis subsp. cremoris and the 23S-5S intergenic spacer region (spacer region 2) of S. salivarius and L. lactis subsp. cremoris were sequenced and compared with the spacer regions 1 and 2 of other streptococci. A high degree of intraspecific conservation was observed for S. thermophilus and L. lactis, and very similar sequences were found for S. salivarius and S. thermophilus. Whereas spacer region 1 is highly conserved in the genus Streptococcus sensu-stricto, only the tRNA gene and the rRNA processing stems are highly conserved in the three genera: Streptococcus sensu-stricto, Lactococcus, and Enterococcus. The presence of a unique tRNA(Ala) gene without the 3' terminal CCA sequence seems to be a general feature of the streptococci spacer region 1. A secondary structure model was built to show the interaction between the spacer regions 1 and 2 of S. thermophilus and S. salivarius. The rapid evolution of spacer region 1 in streptococci is in part due to insertions and deletions of small RNA stem/loop structures.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.