Molecular Identification of Iranian isolates of the genus Photorhabdus and Xenorhabdus (Enterobacteriaceae) based on 16S rRNAAbstract : Five bacterial strains of Photorhabdus and six strains of Xenorhabdus originating from several geographical isolates of entomopathogenic nematodes have been studied moleculary to distinguish their position among the well defined species. Constructed phylogenetic trees based on the sequences of 16S-rRNA showed all of the studied Photorhabdus belong to the P. luminescens subsp. lumondii and Xenorhabdus were identified as X. bovienii, X. nematophilus and X. budapestensis. Among the Steinernema feltiae symbiont?s one isolate named Xenorhabdus sp. IRA22 made a nearly distinct branch in the group and therefore it is possible to represent new species.