Utility of internally transcribed 16S-23S rDNA spacer regions for the definition of Pseudomonas stutzeri genomovars and other Pseudomonas species

Bacteria identified and classified as Pseudomonas stutzeri, on the basis of traditional criteria, are recognized to be markedly heterogeneous, such th at a Systematic phenotypic characterization has not been correlated with ge notypic groupings (i.e. genomovars) based upon DNA-DNA similarities. The in ternally transcribed 16S-23S rDNA spacer (ITS1) regions of P. stutzeri were analysed with respect to the ability of these nucleic acid regions to diff erentiate and identify the genomic groups (i.e. genomovars) of P. stutzeri. The ITS1s of 34 strains of P. stutzeri were amplified by PCR and the PCR p roduct was subjected to RFLP analysis, which allowed the differentiation an d identification of the strains to their respective genomovars. Sequence de termination and analysis of ITS1s supported further the results obtained by RFLP, i.e, nucleotide signatures were identified in strains belonging to d ifferent genomovars. The ITS1s of all strains of P. stutzeri contained the tandem tRNA(lle)/tRNA(Ala) genes and did not exhibit distinct sequence hete rogeneity between different operons of a strain. Phylogenetically informati ve variable sites were located, exclusively, in non-coding regions. The res ults of the RFLP and sequence analysis of ITS1s supported and correlated wi th the phylogenetic relationships estimated from 16S rRNA gene sequence com parisons and DNA-DNA hybridizations, offering an alternative tool for genom ovar and species differentiation.