Applied and Environmental Microbiology (2020) 86 (7 - e02770-19)

Nathaly Alexandre Nascimento, Mary Carmen Torres-Quintero, Samira López Molina, Sabino Pacheco, Tatiany Patrícia Romão, Antonio Pereira-Neves, Mario Soberón, Alejandra Bravo and Maria Helena Neves Lobo Silva-Filha (2020)
Functional Bacillus thuringiensis Cyt1Aa is necessary to synergize Lysinibacillus sphaericus binary toxin (Bin) against bin-resistant and -refractory mosquito species
Applied and Environmental Microbiology 86 (7 - e02770-19)
Abstract: The binary (Bin) toxin from Lysinibacillus sphaericus is effective to mosquito larvae, but its utilization is threatened by the development of insect resistance. Bin toxin is composed of the BinB subunit required for binding to midgut receptors and the BinA subunit that causes toxicity after cell internalization, mediated by BinB. Culex quinquefasciatus resistance to this toxin is caused by mutations that prevent expression of Bin toxin receptors in the midgut. Previously, it was shown that the Cyt1Aa toxin from Bacillus thuringiensis subsp. israelensis restores Bin toxicity to Bin-resistant C. quinquefasciatus and to Aedes aegypti larvae, which are naturally devoid of functional Bin receptors. Our goal was to elucidate the mechanism involved in Cyt1Aa synergism with Bin in such larvae. In vivo assays showed that the mixture of Bin toxin, or its BinA subunit, with Cyt1Aa was effective to kill resistant larvae. However, no specific binding interaction between Cyt1Aa and the Bin toxin, or its subunits, was observed. The synergy between Cyt1Aa and Bin toxins is dependent on functional Cyt1Aa, as demonstrated by using the nontoxic Cyt1AaV122E mutant toxin affected in oligomerization and membrane insertion, which was unable to synergize Bin toxicity in resistant larvae. The synergism correlated with the internalization of Bin or BinA into anterior and medium midgut epithelial cells, which occurred only in larvae treated with wild-type Cyt1Aa toxin. This toxin is able to overcome failures in the binding step involving BinB receptor by allowing the internalization of Bin toxin, or its BinA subunit, into the midgut cells.
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Link to article at publishers website
Database assignments for author(s): Alejandra Bravo

Research topic(s) for pests/diseases/weeds:
biocontrol - natural enemies
Research topic(s) for beneficials or antagonists:
resistance/tolerance/defence of host

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Pest and/or beneficial records:

Beneficial	Pest/Disease/Weed	Crop/Product	Country	Quarant.
	Culex quinquefasciatus
Lysinibacillus sphaericus (entomopathogen)	Culex quinquefasciatus