Isolation and identification of Xenorhabdus and Photorhabdus bacteria associated with entomopathogenic nematodes and their larvicidal activity against Aedes aegypti

Abstract

Background Aedes aegypti is a potential vector of West Nile, Japanese encephalitis, chikungunya, dengue and Zika viruses. Alternative control measurements of the vector are needed to overcome the problems of environmental contamination and chemical resistance. Xenorhabdus and Photorhabdus are symbionts in the intestine of entomopathogenic nematodes (EPNs) Steinernema spp. and Heterorhabditis spp. These bacteria are able to produce a broad range of bioactive compounds including antimicrobial, antiparasitic, cytotoxic and insecticidal compounds. The objectives of this study were to identify Xenorhabdus and Photorhabdus isolated from EPNs in upper northern Thailand and to study their larvicidal activity against Ae. aegypti larvae.ResultsA total of 60 isolates of symbiotic bacteria isolated from EPNs consisted of Xenorhabdus (32 isolates) and Photorhabdus (28 isolates). Based on recA gene sequencing, BLASTN and phylogenetic analysis, 27 isolates of Xenorhabdus were identical and closely related to X. stockiae, 4 isolates were identical to X. miraniensis, and one isolate was identical to X. ehlersii. Twenty-seven isolates of Photorhabdus were closely related to P. luminescens akhurstii and P. luminescens hainanensis, and only one isolate was identical and closely related to P. luminescens laumondii. Xenorhabdus and Photorhabdus were lethal to Ae aegypti larvae. Xenorhabdus ehlersii bMH9.2_TH showed 100% efficiency for killing larvae of both fed and unfed conditions, the highest for control of Ae. aegypti larvae and X. stockiae (bLPA18.4_TH) was likely to be effective in killing Ae. aegypti larvae given the mortality rates above 60% at 72 h and 96 h.ConclusionsThe common species in the study area are X. stockiae, P. luminescens akhurstii, and P. luminescens hainanensis. Three symbiotic associations identified included P. luminescens akhurstii-H. gerrardi, P. luminescens hainanensis-H. gerrardi and X. ehlersii-S. Scarabaei which are new observations of importance to our knowledge of the biodiversity of, and relationships between, EPNs and their symbiotic bacteria. Based on the biological assay, X. ehlersii bMH9.2_TH begins to kill Ae. aegypti larvae within 48 h and has the most potential as a pathogen to the larvae. These data indicate that X. ehlersii may be an alternative biological control agent for Ae. aegypti and other mosquitoes.

Survey of entomopathogenic nematodes and associate bacteria in Thailand and their potential to control Aedes aegypti

“…akhurstii is a common complex found in Thailand. These associations are consistent with a previous study in Thailand (Fukruksa et al, ; Tailliez et al, ; Thanwisai et al, ). In addition, H. indica from Australia and Israel was reported as the host for P. luminescens subsp.…”

“…Several species of symbiotic bacteria and their EPNs, including S. scarabiae / X. ehlersii , S. kushidai / X. japonica and H. zealandica / P. temperata subsp. temperata , have been reported as new records and associations in Thailand (Fukruksa et al, ; Muangpat et al, ; Vitta et al, ). The most common species of EPNs identified in this study was S. surkhetense , which was associated with X. stockiae .…”

“…According to previous studies on EPNs and symbiotic bacteria in Thailand, 12 species of EPNs and seven species of bacteria associated with these EPNs have been found in several regions (Fukruksa et al, ; Muangpat et al, ; Thanwisai et al, ; Vitta et al, ; Yooyangket et al, ). In earlier studies on the diversity of EPNs and symbiotic bacteria, the common symbiotic relationship between Steinernema and Xenorhabdus was found to be S. websteri associated with X. stockiae , whereas a mutual relationship was found between Heterorhabditis and Photorhabdus ( H. indica associated with P. luminescens subsp.…”

“…aegypti and Ae. albopictus larvae were susceptible to symbiotic bacteria, with high mortality after exposure to P. luminescens , X. nematophila (da Silva et al, ), X. stockiae (bNBP22.2_TH), X. indica (bKK26.2_TH) (Vitta et al, ), X. ehlersii bMH9.2_TH, X. stockiae (bLPA18.4_TH) (Fukruksa et al, ), X. stockiae (bNN112.3_TH), and P. luminescens subsp. akhurstii (bNN121.4_TH) (Yooyangket et al, ).…”

“…Cell suspensions of Xenorhabdus and Photorhabdus have also been reported as biocontrol agents against Aedes spp. in the laboratory (Da Silva et al, ; Fukruksa et al, ; Vitta et al, ; Yooyangket et al, ). Therefore, Xenorhabdus and Photorhabdus are interesting alternative larvicides for controlling Aedes mosquitoes.…”