Cytopathological effects of Bacillus sphaericus Cry48Aa/Cry49Aa toxin on binary toxin-susceptible and -resistant Culex quinquefasciatus larvae

Janaina Viana de Melo, Gareth Wyn Jones, Colin Berry, Romero Henrique Teixeira Vasconcelos, Cláudia Maria Fontes de Oliveira, André Freire Furtado, Christina Alves Peixoto, Maria Helena Neves Lobo Silva-Filha

Research output: Contribution to journalArticle (Academic Journal)peer-review

14 Citations (Scopus)


The Cry48Aa/Cry49Aa mosquitocidal two-component toxin was recently characterized from Bacillus sphaericus strain IAB59 and is uniquely composed of a three-domain Cry protein toxin (Cry48Aa) and a binary (Bin) toxin-like protein (Cry49Aa). Its mode of action has not been elucidated, but a remarkable feature of this protein is the high toxicity against species from the Culex complex, besides its capacity to overcome Culex resistance to the Bin toxin, the major insecticidal factor in B. sphaericus-based larvicides. The goal of this work was to investigate the ultrastructural effects of Cry48Aa/Cry49Aa on midgut cells of Bin-toxin-susceptible and -resistant Culex quinquefasciatus larvae. The major cytopathological effects observed after Cry48Aa/Cry49Aa treatment were intense mitochondrial vacuolation, breakdown of endoplasmic reticulum, production of cytoplasmic vacuoles, and microvillus disruption. These effects were similar in Bin-toxin-susceptible and -resistant larvae and demonstrated that Cry48Aa/Cry49Aa toxin interacts with and displays toxic effects on cells lacking receptors for the Bin toxin, while B. sphaericus IAB59-resistant larvae did not show mortality after treatment with Cry48Aa/Cry49Aa toxin. The cytopathological alterations in Bin-toxin-resistant larvae provoked by Cry48Aa/Cry49Aa treatment were similar to those observed when larvae were exposed to a synergistic mixture of Bin/Cry11Aa toxins. Such effects seemed to result from a combined action of Cry-like and Bin-like toxins. The complex effects caused by Cry48Aa/Cry49Aa provide evidence for the potential of these toxins as active ingredients of a new generation of biolarvicides that conjugate insecticidal factors with distinct sites of action, in order to manage mosquito resistance.

Original languageEnglish
Pages (from-to)4782-9
Number of pages8
JournalApplied and Environmental Microbiology
Issue number14
Publication statusPublished - Jul 2009


  • Animals
  • Bacillus/metabolism
  • Bacterial Toxins/pharmacology
  • Culex/drug effects
  • Gastrointestinal Tract/drug effects
  • Insecticides/pharmacology
  • Larva/drug effects
  • Organelles/drug effects
  • Survival Analysis


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