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1 INRA;
2 Universite Montpellier 2
3 E-mail: tailliez{at}univ-montp2.fr
We used the information from a set of concatenated sequences from four genes (recA, gyrB, dnaN and gltX) to investigate the phylogeny of the genera Photorhabdus and Xenorhabdus (entomopathogenic bacteria associated with nematodes of the genera Heterorhabditis and Steinernema, respectively). The robustness of the phylogenetic tree obtained by this multigene approach was significantly better than that obtained by a single gene approach. The comparison of the topologies of single gene phylogenetic trees highlighted discrepancies which have implications for the classification of strains and new isolates; in particular, we propose the transfer of P. luminescens subsp. thracensis to 'P. temperata subsp. thracensis subsp. nov.'. We found that, within the genus Xenorhabdus, strains or isolates that shared less than 97% of nucleotide identity (NI), calculated on the concatenated sequences of the four gene fragments (recA, gyrB, dnaN and gltX) encompassing 3395 nucleotides, did not belong to the same species. Thus, at the 97% NI cutoff, we confirm the current 20 Xenorhabdus species and we propose the description of a novel Xenorhabdus species, X. vietnamensis sp. nov. (type strain VN01T). Within each of the three current Photorhabdus species: P. asymbiotica, P. luminescens and P. temperata, strains or isolates which shared less than 97% of nucleotide identity (NI) did not belong to the same subspecies. Comparisons of the four gene fragments plus the rplB gene fragment analysed separately led us to propose four novel subspecies: P. luminescens subsp. caribbeanensis subsp. nov. (type strain HG29T), P. luminescens subsp. hainanensis subsp. nov. (type strain C8404T), P. temperata subsp. khanii subsp. nov. (type strain C1T), and P. temperata subsp. tasmaniensis subsp. nov. (type strain T327T).
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