Identification of symbiotic bacteria Xenorhabdus and Photorhabdus associated with entomopathogenic nematodes (Steinernema and Heterorhabditis)

Isolation and molecular identification of 123 mutualistic bacterial isolate associated with entomopathogenic nematodes recovered from The Republic of South Africa soil samples were carried out. Species identification and phylogenetic analysis of all bacterial isolates were subsequently performed on the basis of RecA sequences. A 890 bp region of the recA gene was amplified by PCR using the following primers: recA-F (5´-GCTATTGATGAAAATAAACA-3´) and recA-R (5´-RATTTTRTCWCCRTTRTAGCT-3´). RecA analyses showed that 53 of Xenorhabdus bacterial strains isolated from the genus Steinernema were all closely related to each other and most distantly related to known species. SGI-145 was similar to X. miraniensis and 16 strains were belong to X. khoisanae species. It was determined that 5 of the strains (SGI-220, SGI-226, SGI-221, SGI-238 and SGI-249) were similar to X. indica and 3of the strains (NWGA-7, NWGA-33 and SGI-145-b) were closely related to X. bovienii species. Rec A sequences resolved all Photorhabdus species. Most of the novel strains was belong to P. luminescens species but might represent novel subspecies. Only one isolate (SGI-193) was identified as P. luminescens subsp. thracensis. As a result, the data obtained from molecular analyses showed that there are at least one new Xenorhabdus species and several new subspecies belong to Photorhabdus luminescens species in South African bacterial isolates.