Photorhabdus heterorhabditis subsp. aluminescens subsp. nov., Photorhabdus heterorhabditis subsp. heterorhabditis subsp. nov., Photorhabdus australis subsp. thailandensis subsp. nov., Photorhabdus australis subsp. australis subsp. nov., and Photorhabdus aegyptia sp. nov. isolated from Heterorhabditis entomopathogenic nematodes

Abstract

Three Gram-stain-negative, rod-shaped, non-spore-forming bacteria, BA1^T, Q614^T and PB68.1^T, isolated from the digestive system of <i>Heterorhabditis</i> entomopathogenic nematodes, were biochemically and molecularly characterized to clarify their taxonomic affiliations. The 16S rRNA gene sequences of these strains suggest that they belong to the Gammaproteobacteria, to the family <i>Morganellacea</i>, and to the genus <i>Photorhabdus</i>. Deeper analyses using whole genome-based phylogenetic reconstructions suggest that BA1^T is closely related to <i>Photorhabdus akhursti</i>, that Q614^T is closely related to <i>Photorhabdus heterorhabditis,</i> and that PB68.1^T is closely related to <i>Photorhabdus australis. In silico</i> genomic comparisons confirm these observations: BA1^T and <i>P. akhursti</i> 15138^T share 68.8 % digital DNA-DNA hybridization (dDDH), Q614^T and <i>P. heterorhabditis</i> SF41^T share 75.4 % dDDH, and PB68.1^T and <i>P. australis</i> DSM 17609^T share 76.6 % dDDH. Physiological and biochemical characterizations reveal that these three strains also differ from all validly described <i>Photorhabdus</i> species and from their more closely related taxa, contrary to what was previously suggested. We therefore propose to classify BA1^T as a new species within the genus <i>Photorhabdus</i>, Q614^T as a new subspecies within <i>P. heterorhabditis,</i> and PB68.1^T as a new subspecies within <i>P. australis</i>. Hence, the following names are proposed for these strains: <i>Photorhabdus aegyptia</i> sp. nov. with the type strain BA1^T(=DSM 111180^T=CCOS 1943^T=LMG 31957^T), <i>Photorhabdus heterorhabditis</i> subsp<i>. aluminescens</i> subsp. nov. with the type strain Q614^T (=DSM 111144^T=CCOS 1944^T=LMG 31959^T) and <i>Photorhabdus australis</i> subsp<i>. thailandensis</i> subsp. nov. with the type strain PB68.1^T (=DSM 111145^T=CCOS 1942^T). These propositions automatically create <i>Photorhabdus heterorhabditis</i> subsp<i>. heterorhabditis</i> subsp. nov. with SF41^T as the type strain (currently classified as <i>P. heterorhabditis</i>) and <i>Photorhabdus australis</i> subsp. <i>australis</i> subsp. nov. with DSM17609^T as the type strain (currently classified as <i>P. australis</i>).