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The great potential of entomopathogenic bacteria Xenorhabdus and Photorhabdus for mosquito control: a review - PubMed

  • ️Wed Jan 01 2020

Review

The great potential of entomopathogenic bacteria Xenorhabdus and Photorhabdus for mosquito control: a review

Wellington Junior da Silva et al. Parasit Vectors. 2020.

Abstract

The control of insects of medical importance, such as Aedes aegypti and Aedes albopictus are still the only effective way to prevent the transmission of diseases, such as dengue, chikungunya and Zika. Their control is performed mainly using chemical products; however, they often have low specificity to non-target organisms, including humans. Also, studies have reported resistance to the most commonly used insecticides, such as the organophosphate and pyrethroids. Biological control is an ecological and sustainable method since it has a slow rate of insect resistance development. Bacterial species of the genera Xenorhabdus and Photorhabdus have been the target of several research groups worldwide, aiming at their use in agricultural, pharmaceutical and industrial products. This review highlights articles referring to the use of Xenorhabdus and Photorhabdus for insects and especially for mosquito control proposing future ways for their biotechnological applicability. Approximately 24 species of Xenorhabdus and five species of Photorhabdus have been described to have insecticidal properties. These studies have shown genes that are capable of encoding low molecular weight proteins, secondary toxin complexes and metabolites with insecticide activities, as well as antibiotic, fungicidal and antiparasitic molecules. In addition, several species of Xenorhabdus and Photorhabdus showed insecticidal properties against mosquitoes. Therefore, these biological agents can be used in new control methods, and must be, urgently considered in short term, in studies and applications, especially in mosquito control.

Keywords: Aedes aegypti; Biological control; Entomopathogenic bacteria; Mosquito-borne arboviruses; Photorhabdus luminescens; Xenorhabdus nematophila.

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Conflict of interest statement

The authors declare that they have no competing interests.

Figures

Fig. 1
Fig. 1

Schematic drawing of the entomopathogenic nematode cycle, with the Photorhabdus and Xenorhabdus bacteria, demonstrating their symbiosis. The nematodes roam freely in the soil until they find a host insect, in the scheme represented by a caterpillar. The nematodes, when entering the host and settling in the hemocoel, release the bacteria through defecation or regurgitation. The bacteria proliferate in the hemocoel and become infectious, when they release toxic molecules to the host, leading to their death. Nematodes use the host’s carcass to reproduce and return to the habitat carrying the bacteria, restarting the cycle until the nematodes find a new host insect

Fig. 2
Fig. 2

Schematic drawing of toxins and mode of action of some compounds produced by the bacteria Xenorhabdus and Photorhabdus. Xenorhabdus can produce toxin complexes that induce immunosuppression in insects by inhibiting eicosanoid synthesis. The Xenorhabdus lipoprotein toxin produced by X. innexi has toxic properties against culicids. Photorhabdus also produces toxin complexes, which have activity directly in the intestinal epithelium of insects, leading to their destruction. Make caterpillars floppy causes apoptosis in hemocytes in the hemocoel. Photorhabdus virulence cassettes, encode genes that are toxic action against some species of lepidopterous. Insect-related protein is highly toxic and is similar to δ endotoxins of Bacillus thuringiensis. Photorhabdus can produce toxins that directly affect Phospholipase A2, while Xenorhabdus produces toxins that inhibit phenoloxidase produced through prophenoloxidase, directly affecting the insect’s immune system. Abbreviations: Xr, Xenorhabdus; Tcs, toxin complexes; Xlt, Xenorhabdus lipoprotein toxin; Pr, Photorhabdus; Mcf, make caterpillars floppy; Pvc, Photorhabdus virulence cassettes; Pir, insect-related protein; PO, phenoloxidase; proPO, prophenoloxidase

Fig. 3
Fig. 3

Schematic drawing summarizing the mechanisms related to Xenorhabdus and Photorhabdus for the control of culicids. 1Xenorhabdus and Photorhabdusin increase the toxic effect of Cry4Ba derived from Bacillus thuringiensis var. israliensis against Aedes aegypti.2Xenorhabdus liprotein toxin has the ability to create pores on the apical surface of cells in the anterior midgut of mosquitoes but in the anterior portion of the middle intestine, causing cell death. 3Xenorhabdus nematophila (Xrn) secretes proteins and secondary metabolites that are effective in the control of culicids, while Photorhabdus asymbiotica (Pra) produce PirAB proteins, which have already been tested on Aedes albopictus, Aedes aegypti and are toxic even by oral administration. Abbreviations: Xr, Xenorhabdus; Pr, Photorhabdus; Bti, Bacillus thuringiensis var. israliensis; Xlt, Xenorhabdus lipoprotein toxin; Xrn, Xenorhabdus nematophila; Pra, Photorhabdus asymbiotica

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