Evidence for conserved tRNA genes in the 16S-23S rDNA spacer sequence and two rrn operons of Xylella fastidiosa

The 16S-23S rDNA spacer of the type strain (ATCC 35879) of Xylella fastidio sa was amplified by PCR, cloned, and sequenced. The spacer sequence (455 bp ) contains two tRNA (tRNA(ala) and tRNA(ile)) genes. Identical tRNA genes w ere also found in the 16S-23S spacer sequences of all the 51 strains of X. fastidiosa retrieved from the GenBank database. At this particular locus, t he gene order of tRNA(ala) - tRNA(ile) is conserved among all the studied s trains of Xylella and Xanthomonas, and different from those of other bacter ia. Sequence analysis showed that Xanthomonas is the most closely related g enus. Results from restriction endonuclease analysis suggested the presence of two rrn operons in the genome of a Xylella fastidiosa Pierce's disease strain.