title: Histopathological and ultrastructural effects of delta-endotoxins of Bacillus thuringiensis serovar israelensis in the midgut of Simulium pertinax larvae (Diptera, Simuliidae).
abstract: The bacterium Bacillus thuringiensis (Bt) produces parasporal crystals containing delta-endotoxins responsible for selective insecticidal activity on larvae. Upon ingestion, these crystals are solubilized in the midgut lumen and converted into active toxins that bind to receptors present on the microvilli causing serious damage to the epithelial columnar cells. We investigated the effect of these endotoxins on larvae of the Simulium pertinax, a common black fly in Brazil, using several concentrations during 4 h of the serovar israelensis strain IPS-82 (LFB-FIOCRUZ 584), serotype H-14 type strain of the Institute Pasteur, Paris. Light and electron microscope observations revealed, by time and endotoxin concentration, increasing damages of the larvae midgut epithelium. The most characteristic effects were midgut columnar cell vacuolization, microvilli damages, epithelium cell contents passing into the midgut lumen and finally the cell death. This article is the first report of the histopathological effects of the Bti endotoxins in the midgut of S. pertinax larvae and the data obtained may contribute to a better understanding of the mode of action of this bacterial strain used as bioinsecticide against black fly larvae.
authors.affiliation: Departamento de Bacteriologia, Instituto Oswaldo Cruz-Fiocruz, Av. Brasil 4365, 21045-900 Rio de Janeiro, RJ, Brazil. ccavados@ioc.fiocruz.br
authors.forename: C F G
authors.initials: CF
authors.lastname: Cavados
authors.forename: S
authors.initials: S
authors.lastname: Majerowicz
authors.forename: J Q
authors.initials: JQ
authors.lastname: Chaves
authors.forename: C J P C
authors.initials: CJ
authors.lastname: Araújo-Coutinho
authors.forename: L
authors.initials: L
authors.lastname: Rabinovitch
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000494:pharmacology*; D001427:Bacterial Toxins / Q000494:pharmacology*; D004064:Digestive System / Q000187:drug effects* / Q000648:ultrastructure; D004731:Endotoxins / Q000494:pharmacology*; D006460:Hemolysin Proteins; D007306:Insecticides / Q000494:pharmacology*; D007814:Larva / Q000187:drug effects / Q000648:ultrastructure; D008854:Microscopy, Electron; D010572:Pest Control, Biological; D012843:Simuliidae / Q000187:drug effects* / Q000648:ultrastructure
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D001427:Bacterial Toxins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; C030956:insecticidal crystal protein, Bacillus Thuringiensis