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Viral diseases like yellow fever, dengue, and Zika have an alarming impact on public health. These diseases can be transmitted by Aedes mosquito species, such as Ae. albopictus, which is now found in many countries outside its original range. Xenorhabdus and Photorhabdus spp. are enteric bacterial symbionts of insect-preying nematodes and are known to produce an array of natural products with various activities including larvicidal activity. In this study, the effects of natural products produced by four Xenorhabdus and one Photorhabdus bacteria on the ovipositional behavior of Ae. albopictus mosquitoes were assessed. Utilizing a binary choice assay in insect cages, gravid female mosquitoes were presented with two oviposition cups containing water supplemented with varying concentrations of bacterial supernatants (50–1% concentrations) versus control medium. After 72 h, the eggs deposited on filter papers were counted. The oviposition attractant index (OAI) feature of the bacterial supernatant was evaluated using the number of eggs laid in the cups. Notably, all tested supernatants exhibited concentration-dependent deterrence of oviposition. Xenorhabdus cabanillasii displayed the strongest deterrent effect, inhibiting egg-laying at 50–5% concentrations (OAI: − 0.87 to − 0.35), followed by X. nematophila (50–10%, OAI: − 0.82 to − 0.52). Xenorhabdus szentirmaii, X. doucetiae, and P. kayaii showed significant deterrence at ≥ 20% concentrations. Using promoter exchange mutants generated by the easyPACId approach, fabclavine from X. szentirmaii was identified as the bioactive compound with evident deterrent effects. Such deterrents targeting egg-laying could be valuable for controlling populations by disrupting their breeding in suitable habitats. [ABSTRACT FROM AUTHOR]

Natural products have been proven to be important starting points for the development of new drugs. Bacteria in the genera Photorhabdus and Xenorhabdus produce antimicrobial compounds as secondary metabolites to compete with other organisms. Our study is the first comprehensive study screening the anti-protozoal activity of supernatants containing secondary metabolites produced by 5 Photorhabdus and 22 Xenorhabdus species against human parasitic protozoa, Acanthamoeba castellanii, Entamoeba histolytica, Trichomonas vaginalis, Leishmania tropica and Trypanosoma cruzi, and the identification of novel bioactive antiprotozoal compounds using the easyPACId approach (easy Promoter Activated Compound Identification) method. Though not in all species, both bacterial genera produce antiprotozoal compounds effective on human pathogenic protozoa. The promoter exchange mutants revealed that antiprotozoal bioactive compounds produced by Xenorhabdus bacteria were fabclavines, xenocoumacins, xenorhabdins and PAX peptides. Among the bacteria assessed, only P. namnaoensis appears to have acquired amoebicidal property which is effective on E. histolytica trophozoites. These discovered antiprotozoal compounds might serve as starting points for the development of alternative and novel pharmaceutical agents against human parasitic protozoa in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Larvicidal and ovidical activities of bacterial CFS are dose and species dependent. • Xenorhabdus bacterial metabolites have ovicidal effects on Aedes aegypti eggs. • Fabclavines are highly toxic against mosquito larvae. Aedes -transmitted arboviral infections such as Dengue, Yellow Fever, Zika and Chikungunya are increasing public health problems. Xenorhabdus and Photorhabdus bacteria are promising sources of effective compounds with important biological activities. This study investigated the effects of cell-free supernatants of X. szentirmaii , X. cabanillasii and P. kayaii against Ae. aegypti eggs and larvae and identified the bioactive larvicidal compound in X. szentirmaii using The EasyPACId method. Among the three tested bacterial species, X. cabanillasii exhibited the highest (96%) egg hatching inhibition and larvicidal activity (100% mortality), whereas P. kayaii was the least effective species in our study. EasyPACId method revealed that bioactive larvicidal compound in the bacterial supernatant was fabclavine. Fabclavines obtained from promoter exchange mutants of different bacterial species such as X. cabanillasii, X. budapestensis, X. indica , X. szentirmaii, X. hominckii and X. stockiae were effective against mosquito larvae. Results show that these bacterial metabolites have potential to be used in integrated pest management (IPM) programmes of mosquitoes. [ABSTRACT FROM AUTHOR]

• Bacterial metabolites of Xenorhabdus enter Tetranychus urticae adults through cuticle. • Predatory mites were less affected by the bacterial metabolites than T. urticae. • Eggs of predatory mites were resistant to X. szentirmaii or X. nematophila supernatant. • Bacterial supernatants killed 18.5%-39.2% of mobile stages of predatory mites. • Long legs and thick cuticle of predatory mites reduce their contact with metabolites. The bacterial metabolites in supernatants of Xenorhabdus species have acaricidal activity, but this mode of entry into mites has not yet been elucidated. Herein, we report on the possible mode of entry of Xenorhabdus szentirmaii and Xenorhabdus nematophila supernatants into Tetranychus urticae (Acari: Tetranychidae) adult females. We also assessed the toxicity of the supernatants against the developmental stages of the predatory mites, Phytoseiulus persimilis and Neoseiulus californicus (Acari: Phytoseiidae). Experiments were conducted at 25 ± 1 °C, 70 ± 5% relative humidity, and 16:8h light:dark conditions. Our data showed that the bioactive acaricidal compound is most effective (86.5 to 89% mortality) when the entire integument of T. urticae comes in contact with it compared to contact of the ventral side only (26.5–34%). Against P. persimilis and N. californicus at 6 days post-application (dpa), the eggs were not affected by the X. szentirmaii or X. nematophila supernatant, whereas mortality of the mobile stages (larva, protonymph, deutonymph, adult) was 18.5% to 39.2%. Overall, the predatory mites were less affected by the bacterial metabolites than T. urticae. We hypothesize that the differences in morphology such as longer legs and thicker cuticle, as well as the diet of the predatory mites, reduce the contact of the body parts to the supernatant-treated surfaces. We need to isolate, identify, and characterize the X. szentirmaii and X. nematophila metabolite(s) and demonstrate efficacy to pestiferous mites and safety to plants, non-target organisms and the environment before it can be used as an acaricide. [ABSTRACT FROM AUTHOR]