Molecular characterization of DNA encoding 23S rRNA and 16S–23S rRNA intergenic spacer regions ofAeromonas hydrophila

Amplification of the gene encoding 23S rRNA of Aeromonas hydrophila by polymerase chain reaction, with primers complementary to conserved regions of 16S and the 3'-end of 23S rRNA genes, resulted in a DNA fragment of approximately 3 kb. This fragment was cloned in Escherichia coli, and its nucleotide sequence determined. The region encoding 23S rRNA shows high homology with the published sequences of 23S rRNA from other members of the gamma division of Proteobacteria. The sequence of the intergenic spacer region, between the 16S and 23S rRNA genes, was determined in five clones. Three types of spacer were identified: two clones were identical and encoded tRNA(Ile) and tRNA(Ala) while the remaining three clones contained tRNA(Glu), only two had the same spacer sequences. This variation in sequence indicates that the different clones may be derived from different ribosomal RNA operons.