Showing papers by "Roger Frutos published in 1996"

Binding of Bacillus thuringiensis Cry1 Toxins to the Midgut Brush Border Membrane Vesicles of Chilo suppressalis (Lepidoptera: Pyralidae): Evidence of Shared Binding Sites.

Abstract: Binding and competition among Cry1Aa, Cry1Ac, and Cry1Ba toxins were analyzed quantitatively in vitro by using (sup125)I-labeled activated toxins and brush border membrane vesicles isolated from Chilo suppressalis larval midguts. The three toxins bound specifically to the midgut brush border membrane vesicles. Direct binding experiments showed that Cry1Aa and Cry1Ba recognized a single class of binding sites with different affinities, whereas Cry1Aa recognized two classes of binding sites, one with a high affinity and a low concentration and the other with a lower affinity but higher concentration. Competition experiments showed that toxins Cry1Ac and Cry1Ba shared a binding site in the C. suppressalis midgut membranes and that this site was also the low-affinity binding site for Cry1Aa.

Influence of the 20-kDa protein from Bacillus thuringiensis ssp. israelensis on the rate of production of truncated Cry1C proteins

Abstract: The potential role of a molecular chaperone on the rate of production of extensively altered Bacillus thuringiensis Cry 1C proteins was investigated. Analysis of the proteins produced by the recombinant B. thuringiensis strains showed that the truncated proteins were produced at a low rate. Expression of the 20-kDa protein gene from B. thuringiensis ssp. israelensis in tandem with the truncated-cry1C genes led to the production of a greater amount of proteins. The formation of inclusion bodies, however, did not occur even when the 20-kDa protein gene was expressed.

Infectivity and complete nucleotide sequence of the genome of a genetically distinct strain of maize streak virus from Reunion Island.

Abstract: A complete infectious genome of an isolate of maize streak subgroup 1 geminivirus from Reunion Island (MSV-R) was cloned and sequenced. Using anAgrobacterium tumefaciens Ti plasmid delivery system, the cloned 2.7 kb circular DNA was shown to be infectious in maize. The agroinfected virus could be transmitted byCicadulina mbila, the most common vector species of MSV in Reunion. Analysis of open reading frames (ORFs) revealed seven potential coding regions including the 4 ORFs conserved in all geminiviruses infecting monocotyledonous plants, the 2 on the viral “+” strand (MP, CP), and the 2 on the complementary “−” strand (RepA, RepB). The nucleotide sequence of MSV-R was compared to previously determined sequence of three African clones from Nigeria (MSV-N), Kenya (MSV-K), and South Africa (MSV-S). More similarity was found between the African clones (97.0–97.3%) than between these and MSV-R (94.4–95.3%). Nucleotide substitutions were frequent in the large intergenic region, particularly in and around the most likely TATA box for the complementary sense genes, and in the 5′ end of ORF V1. The comparison of the predicted peptide sequences of the proteins encoded by ORFs MP, RepA and RepB confirmed the higher similarity between the African clones (97.8–99.3%) than between these and MSV-R (95.1–97.1%). However the amino acid sequences of the protein encoded by ORF CP (capsid protein) were very conserved among all the 4 clones, suggesting a high selection pressure on this ORF.

Activity of natural toxins against the silverleaf whitefly, Bemisia argentifolii, using a novel feeding bioassay system

Abstract: An assay system was developed for the adult silverleaf whitefly, #Bemisia argentifolii# Bellows & Perring (Homoptera : Aleyrodidae). This practical device was constructed from standard disposable laboratory materials. Whiteflies were harvested directly from the leaf and into a collection vial by vacuum aspiration, minimizing physical damage to the insect. Insects were fed throueh a cellulose mixed-ester membrane on a diet of 20-27% sucrose alone or sucrose in an extract of zucchini (#Curcurbita moschata# Duchense). Mortality and honeydew production were scored. At 22-25 °C and 50-55%, relative humidity, control mortality generally remained at or below 15% during a 48 h assay period. The bioassay system was first tested using the insecticide, Imidacloprid, then used to screen a number of natural products with potential insecticidal activity against the whitefly. Destruxins extracted from the entornopathogenic fungus, #Metarhizium anisopliae#, and the natural insccticide/nematicide, Ivermectin, as well as bee venom and two of its components, melittin and phospholipase A,, were found to be toxic to #B. argentifolii#. Five lectins, #Bacillus thuringiensis# toxins, gossypol, an extract of #Paeciliomyces fumosoroseus#, wasp and scorpion venom, and a trypsin inhibitor were not found to be insecticidal to adult #B. argentifolii#. (Resume d'auteur)