New insight into diversity in the genus Xenorhabdus, including the description of ten novel species

Abstract

We investigated the diversity of a collection of 76Xenorhabdusstrains, isolated from at least 27 species ofSteinernemanematodes and collected in 32 countries, using three complementary approaches: 16S rRNA gene sequencing, molecular typing and phenotypic characterization. The 16S rRNA gene sequences of theXenorhabdusstrains were highly conserved (similarity coefficient >95 %), suggesting that the common ancestor of the genus probably emerged between 250 and 500 million years ago. Based on comparisons of the 16S rRNA gene sequences, we identified 13 groups and seven unique sequences. This classification was confirmed by analysis of molecular typing profiles of the strains, leading to the classification of new isolates into theXenorhabdusspecies described previously and the description of ten novelXenorhabdusspecies:Xenorhabdus cabanillasiisp. nov. (type strain USTX62T=CIP 109066T=DSM 17905T),Xenorhabdus doucetiaesp. nov. (type strain FRM16T=CIP 109074T=DSM 17909T),Xenorhabdus griffiniaesp. nov. (type strain ID10T=CIP 109073T=DSM 17911T),Xenorhabdus hominickiisp. nov. (type strain KE01T=CIP 109072T=DSM 17903T),Xenorhabdus koppenhoeferisp. nov. (type strain USNJ01T=CIP 109199T=DSM 18168T),Xenorhabdus kozodoiisp. nov. (type strain SaVT=CIP 109068T=DSM 17907T),Xenorhabdus mauleoniisp. nov. (type strain VC01T=CIP 109075T=DSM 17908T),Xenorhabdus miraniensissp. nov. (type strain Q1T=CIP 109069T=DSM 17902T),Xenorhabdus romaniisp. nov. (type strain PR06-AT=CIP 109070T=DSM 17910T) andXenorhabdus stockiaesp. nov. (type strain TH01T=CIP 109067T=DSM 17904T). TheXenorhabdusstrains studied here had very similar phenotypic patterns, but phenotypic features nonetheless differentiated the following species:X. bovienii,X. cabanillasii,X. hominickii,X. kozodoii,X. nematophila,X. poinariiandX. szentirmaii. Based on phenotypic analysis, we identified two major groups of strains. Phenotypic group GAcomprised strains able to grow at temperatures of 35–42 °C, whereas phenotypic group GBcomprised strains that grew at temperatures below 35 °C, suggesting that someXenorhabdusspecies may be adapted to tropical or temperate regions and/or influenced by the growth and development temperature of their nematode host.