DIVERSITY AND GENETIC RELATEDNESS WITHIN GENERA XANTHOMONAS AND STENOTROPHOMONAS USING RESTRICTION-ENDONUCLEASE SITE DIFFERENCES OF PCR-AMPLIFIED 16S RIBOSOMAL-RNA GENE

Restriction maps of PCR-amplified 16s rRNA genes (rrs for ribosomal rR NA small subunit) were prepared and compared for 43 Xanthomonas and St enotrophomonas strains belonging to representative DNA-DNA similarity groups. Nineteen restriction fragment length polymorphisms (RFLPs) wer e distinguished, forming two main clusters: one contained all Xanthomo nas species, the other contained strains of Stenotrophomonas spp. (for merly named X. maltophilia). The genera Xanthomonas and Stenotrophomon as appeared to form a coherent group excluding Xylella fastidiosa. The rrs RFLP permitted to differentiate X. fragariae, X. oryzae, X. axono podis, X. populi pv. populi from most pathovars of X. campestris. The latter species had very closely related patterns, contrary to X. albil ineans, X. campestris pv. hyacinthi and pv. graminis, and a X. campest ris strain (isolated from Saccharum officinarum, Guadeloupe) whic form ed a more distinct subcluster. All genospecies of Stenotrophomonas had different rrs patterns, and appeared to form a less coherent taxon. R elationships between the percentage of DNA-DNA hybridization and the r ate of nucleotide substitution in rrs confirmed the clear delineation of the two genera.