title: Selection and characterisation of an HD1-like Bacillus thuringiensis isolate with a high insecticidal activity against Spodoptera littoralis (Lepidoptera: Noctuidae).
abstract: BACKGROUND
  Spodoptera littoralis (Boisduval) larvae are known by their susceptibility to Bacillus thuringiensis subsp. aizawai strains. In order to prevent the appearance of B. thuringiensis (Bt) resistance and to develop economical Bt-based biopesticides, the selection and the characterisation of a B. thuringiensis isolate toxic against S. littoralis larvae and overproducing δ-endotoxins were investigated.
  
  
  RESULTS
  Among 124 Tunisian B. thuringiensis isolates assessed against S. littoralis larvae, four isolates showed toxicity similar to and higher than the toxicity of the aizawai strain HD133 and the kurstaki strain HD1 respectively. The plasmid pattern of the selected isolates was similar to that of HD1. Polymerase chain reaction (PCR) analysis using specific primers revealed that these isolates present different gene contents. The only detected gene encoding Spodoptera-specific toxin was cry9. The selected isolates were found to produce bipyramidal and cubic crystals. The assessment of δ-endotoxin production by these isolates showed that BUPM28 produced 43.71 and 80.81% more δ-endotoxin than HD1 and HD133 respectively. The application of osmotic or heat shock stress on the BUPM28 isolate made it possible to enhance δ-endotoxin production by 22 and 23% respectively.
  
  
  CONCLUSIONS
  On the basis of its potent insecticidal activity and its high level of δ-endotoxin production, the BUPM28 isolate can be considered to be an effective alternative for the control of S. littoralis.
authors.affiliation: Laboratory of Plant Protection and Improvement (Biopesticides Team), Centre of Biotechnology of Sfax, Sfax University, Sfax, Tunisia.
authors.forename: Hichem
authors.initials: H
authors.lastname: Azzouz
authors.forename: Jihene
authors.initials: J
authors.lastname: Kebaili-Ghribi
authors.forename: Dalel
authors.initials: D
authors.lastname: ben Farhat-Touzri
authors.forename: Fatma
authors.initials: F
authors.lastname: Daoud
authors.forename: Ines
authors.initials: I
authors.lastname: Fakhfakh
authors.forename: Slim
authors.initials: S
authors.lastname: Tounsi
authors.forename: Samir
authors.initials: S
authors.lastname: Jaoua
mesh_terms: D000818:Animals; D001413:Bacillus thuringiensis / Q000235:genetics / Q000378:metabolism*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D004731:Endotoxins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D006460:Hemolysin Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology*; D007306:Insecticides; D007814:Larva / Q000187:drug effects; D010572:Pest Control, Biological / Q000379:methods*; D010957:Plasmids / Q000235:genetics; D018411:Spodoptera / Q000187:drug effects
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; D007306:Insecticides; C030956:insecticidal crystal protein, Bacillus Thuringiensis
keywords: Bacillus thuringiensis; Spodoptera littoralis; bioinsecticide production; characterisation; cry genes; toxicity