Entomopathogenic nematodes and their bacterial endosymbionts are commonly used as biological control agents against agricultural pest insects. The bacterial endosymbionts have been screened and assayed for their insecticidal toxin properties, yet their evolutionary and taxonomic diversity is only beginning to emerge. For the present study, strains of Xenorhabdus and Photorhabdus bacteria were retrieved from 82 entomopathogenic nematode isolates. Identification was based on morphological growth characteristics that were exhibited when cultured on Tergitol-7 agar supplemented with 0.004% triphenyltetrazolium chloride, dividing the bacterial isolates into 40 and 42 strains of Xenorhabdus and Photorhabdus respectively. Relationships among the strains were analyzed by generating genomic fingerprints based on the amplification of repetitive DNA (repetitive extragenic palindromic [REP] and BOX element) sequences distributed throughout the chromosome (rep-PCR). The rep-PCR products were analyzed by agarose gel electrophoresis, revealing strain-specific patterns. Analysis of the combined REP and BOX fingerprints showed the formation of 6 distinct clusters that are correlated with the species of nematode from which the bacteria were isolated. However, some strains that were isolated from Steinernema glaseri are dispersed paraphyletically throughout the dendrogram. Other strains formed unique, independent lineages raising the possibility that they represent new species of Xenorhabdus. Rep-PCR may provide an efficient and sensitive diagnostic tool for identifying and characterizing the bacterial endosymbionts of entomopathogenic nematodes.
Species 1: Rhabditida Steinernematidae Steinernema
Species 2: Rhabditida Heterorhabditidae Heterorhabditis
Keywords: Entomopathogenic nematodes, Entomopathogenic bacteria
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