Isolation, bioassay and characterisation of Xenorhabdus sp. SY5, a highly virulent symbiotic bacterium of an entomopathogenic nematode isolated from China

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The entomopathogenic nematodes (EPN), together with their symbiotic bacteria, are obligate and lethal parasites of insects and are applied as biological approaches to pest management. In this paper, we isolated 122 strains of symbiotic bacteria from 23 EPN isolates that were gathered in various soils containing different vegetations from different regions of China. All these isolated bacterial strains showed oral insecticidal activity and/or growth inhibition to the larvae of Ostrinia furnacalis. Among these strains, Xenorhabdus sp. SY5 exhibited high insecticidal activity to O. furnacalis, Plutella xylostella, Mythimna separata, Laphygma exigua and Tenebrio molitor, all of which are important agricultural pests. Xenorhabdus sp. SY5 was isolated from EPN Steinernema sp. SY5. Through DEAE-52 column chromatography, seven toxins were purified from X. sp. SY5. Bioassay results showed that all seven toxins had, to a certain extent, insecticidal activity and/or growth inhibition to O. furnacalis, T. molitor, P. xylostella, M. separata and L. exigua. Our data also showed that each of these toxins had different insecticidal activity and/or growth inhibition against different insect species. The partial toxin gene sequence of X. sp. SY5 was determined, and its deduced amino acid sequence only showed 75, 66 and 65% identities to homologues of EPN symbiotic bacteria Photorhabdus luminescens, Xenorhabdus nematophila and Yersinia mollaretii, respectively. These results suggested that strain SY5 is a highly virulent EPN symbiotic bacterial strain that has a potential value for biological pest control.


International Journal of Fundamental and Applied Nematological Research



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  • Variable sites of the alignment of the partial 16S rDNA gene sequences of Xenorhabdus sp. SY5 and other bacterial strains. Xsp, Xenorhabdus sp. SY5 (HQ231761); Xbs, X. bovienii SM (AB507818); Xbu, X. bovienii USNY95 (DQ205453); Xp, X. poinarii (HQ231760); Xn, X. nematophila (AY286478); Xh, X. hominickii (AB507814). Only 19 variable sites were detected from the alignments with a total of 424 bp in length. Sites where all sequences were identical are not shown. The position of the variable site is indicated vertically in the first three rows. Dots (.) indicate nucleotides identical to the top sequence, and dashes (-) indicate alignment gaps. Identity (%) with Xsp is followed.

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  • DEAE-52 chromatography elution pattern, showing seven insecticidal active peaks. As determined by bioassay, peaks I through VII showed insecticidal activity and/or growth inhibition to the five pest species tested. Solid line, absorbance at 280 nm.

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  • Partial amino acid sequence alignment of the toxic gene from Xenorhabdus sp. SY5 and other bacterial strains. Xsp, X. sp. SY5 XptA1 (HQ231762); Pl, Photorhabdus luminescens TcdA1 (CAE13257); Xn, Xenorhabdus nematophila XptA1 (CAC38401); Ym, Yersinia mollaretii ATCC 43969 (EEQ10066).

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