PCR-RIBOTYPING OF XENORHABDUS AND PHOTORHABDUS ISOLATES FROM THE CARIBBEAN REGION IN RELATION TO THE TAXONOMY AND GEOGRAPHIC-DISTRIBUTION OF THEIR NEMATODE HOSTS

The genetic diversity of symbiotic Xenorhabdus and Photorhabdus bacter ia associated with entomopathogenic nematodes was examined by a restri ction fragment length polymorphism analysis of PCR-amplified 16S rRNA genes (rDNAs). A total of 117 strains were studied, most of which,were isolated from the Caribbean basin after an exhaustive soil sampling. The collection consisted of 77 isolates recovered from entomopathogeni c nematodes in 14 Caribbean islands and of 40 reference strains belong ing to Xenorhabdus and Photorhabdus spp. collected at various localiti es worldwide. Thirty distinctive 16S rDNA genotypes were identified, a nd cluster analysis was used to distinguish the genus Xenorhabdus from the genus Photorhabdus. The genus Xenorhabdus appears more diverse th an the genus Photorhabdus, and for both genera the bacterial genotype diversity is in congruence with the host-nematode taxonomy. The occurr ence of symbiotic bacterial genotypes was related to the ecological di stribution of host nematodes.