title: Evidence of two mechanisms involved in Bacillus thuringiensis israelensis decreased toxicity against mosquito larvae: Genome dynamic and toxins stability.
abstract: Biopesticides based on Bacillus thuringiensis israelensis are the most used and most successful around the world. This bacterium is characterized by a dynamic genome able to win or lose genetic materials which leads to a decrease in its effectiveness. The detection of such phenomena is of great importance to monitor the stability of B. thuringiensis strains in industrial production processes of biopesticides. New local B. thuringiensis israelensis isolates were investigated. They present variable levels of delta-endotoxins production and insecticidal activities against Aedes aegypti larvae. Searching on the origin of this variability, molecular and biochemical analyses were performed. The obtained results describe two main reasons of the decrease of B. thuringiensis israelensis insecticidal activity. The first reason was the deletion of cry4Aa and cry10Aa genes from the 128-kb pBtoxis plasmid as evidenced in three strains (BLB124, BLB199 and BLB506) among five. The second was the early degradation of Cry toxins by proteases in larvae midgut mainly due to some amino acids substitutions evidenced in Cry4Ba and Cry11Aa δ-endotoxins detected in BLB356. Before biological treatment based on B. thuringiensis israelensis, the studies of microflore in each ecosystem have a great importance to succeed pest management programs.
authors.affiliation: Biopesticides Team [L.P.I.P.], Center of Biotechnology of Sfax, University of Sfax, P.O. Box 1177, 3018 Sfax, Tunisia.
authors.forename: Jihen
authors.initials: J
authors.lastname: Elleuch
authors.affiliation: Biopesticides Team [L.P.I.P.], Center of Biotechnology of Sfax, University of Sfax, P.O. Box 1177, 3018 Sfax, Tunisia. Electronic address: raida_zz@yahoo.fr.
authors.forename: Raida
authors.initials: R
authors.lastname: Zribi Zghal
authors.affiliation: Institut de Recherche pour le Développement (IRD), UMR MIVEGEC (UM1-UM2-CNRS 5290-IRD 224) Maladies Infectieuses et Vecteurs, Ecologie, Génétique, Evolution et Contrôle, Laboratoire de Lutte contre les Insectes Nuisibles (LIN), Montpellier, France.
authors.forename: Marie Noël
authors.initials: MN
authors.lastname: Lacoix
authors.affiliation: Institut de Recherche pour le Développement (IRD), UMR MIVEGEC (UM1-UM2-CNRS 5290-IRD 224) Maladies Infectieuses et Vecteurs, Ecologie, Génétique, Evolution et Contrôle, Laboratoire de Lutte contre les Insectes Nuisibles (LIN), Montpellier, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Chandre
authors.affiliation: Biopesticides Team [L.P.I.P.], Center of Biotechnology of Sfax, University of Sfax, P.O. Box 1177, 3018 Sfax, Tunisia.
authors.forename: Slim
authors.initials: S
authors.lastname: Tounsi
authors.affiliation: Department of Biological & Environmental Sciences, Qatar University, P.O. Box 2713, Doha, Qatar.
authors.forename: Samir
authors.initials: S
authors.lastname: Jaoua
mesh_terms: D000330:Aedes / Q000382:microbiology* / Q000502:physiology*; D000818:Animals; D001413:Bacillus thuringiensis / Q000235:genetics / Q000472:pathogenicity*; D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins / Q000235:genetics / Q000633:toxicity; D004731:Endotoxins / Q000235:genetics / Q000633:toxicity; D041981:Gastrointestinal Tract / Q000201:enzymology; D017353:Gene Deletion; D016678:Genome; D042822:Genomic Instability; D006460:Hemolysin Proteins / Q000235:genetics / Q000633:toxicity; D007814:Larva / Q000382:microbiology* / Q000502:physiology*; D020125:Mutation, Missense; D010447:Peptide Hydrolases / Q000378:metabolism; D010957:Plasmids; D059748:Proteolysis; D013534:Survival; D014774:Virulence
chemical_list: D000083722:Bacillus thuringiensis Toxins; D001426:Bacterial Proteins; D004731:Endotoxins; D006460:Hemolysin Proteins; C030956:insecticidal crystal protein, Bacillus Thuringiensis; D010447:Peptide Hydrolases
keywords: Aedes aegypti; Bacillus thuringiensis israelensis; Proteolysis; cry genes content