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

Abstract

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.

Xenorhabdus spp.: An Overview of the Useful Facets of Mutualistic Bacteria of Entomopathogenic Nematodes

“…Although the obtained data confirmed the direct toxicity of the bacteria to definite insect species in nature, e.g., [5,52,66], particular Xenorhabdus bacteria may have wide host range of insect pests. For example, 122 strains of symbiotic bacteria associated with 23 EPNs were gathered from various Chinese localities [67]. These extracted strains displayed oral growth inhibition and/or insecticidal activity against the Ostrinia furnacalis larvae.…”

“…These toxins exhibited, to a certain extent, growth inhibition and/or insecticidal activity to these insect species. The authors [67] stressed the high virulence of this strain as a potential asset for biological pest control.…”