Sensibilité desCulicidae a la β-exotoxine deBacillus thuringiensis

Résumé Cette étude vise à élargir les connaissances du potentiel toxique de la β-exotoxine deB. thuringiensis Berliner sur lesCulicidae et particulièrement surAedes aegypti (L.),Anopheles stephensi (Liston) etCulex pipiens (L.). La toxicité par ingestion de la β-exotoxine deB. thuringiensis H 1 à 1 mg/ml est totale, sur les adultes males et femelles. La sensibilité des stades larvaires est proportionnelle à la concentration. La descendance des adultes, issus de larves traitées à une dose sublétale, présente une sensibilité accrue à l'exotoxine. La β-exotoxine induit un effet retard sur les mues larvaires ainsi que des effets tératogènes à la nymphose.

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Summary The β-exotoxine ofB. thuringiensis H 1 acts as a larvicide and as an adulticide when ingested at high concentrations byAedes aegypti L.,Anopheles stephensi Liston orCulex pipiens L. Sublethal concentrations of β-exotoxin induce a delay of larval moulting and teratological effects on larvae and pupae. After sublethal application of β-exotoxine to larval stage the next larval generation presents an enhanced sensibility to this toxin.

     

Mutations in the mitochondrial split gene COXI are preferentially located in exons: a mapping study of 170 mutants

We have analysed the precise location of a large number (170) of mutations affecting the structural gene for subunit 1 of the cytochrome c oxidase complex. This gene, COXI, is 12.9 kb long and the major part of the sequence (i.e. 11.3 kb) is composed of introns. Several conclusions can be drawn from this study: (1) A significant proportion (84/170) of the mutations cannot be assigned to a single position within the gene by deletion mapping, in spite of clearly being located in it. These mutations are probably large deletions or multiple mutations. (2) Four mutants carry distant double mutations, which have been individually localized. (3) Eighty-two mutants have lesions that are restricted to very short regions of the gene and we therefore conclude that they are most probably due to single hits; amongst these single mutations, 41 are unambiguously located in exons and 28 in introns. This result implies that, at least in this particular split gene, the probability of selection of a mutant phenotype in an exon is, on the average, 13.3 times greater than in an intron, in spite of the existence, within most of these introns, of open reading frames specifying intronic proteins. The evolutionary significance and biological implications of these results are discussed.     

Patulin is a cultivar‐dependent aggressiveness factor favouring the colonization of apples by Penicillium expansum

The blue mould decay of apples is caused by Penicillium expansum and is associated with contamination by patulin, a worldwide regulated mycotoxin. Recently, a cluster of 15 genes (patA–patO) involved in patulin biosynthesis was identified in P. expansum. blast analysis revealed that patL encodes a Cys₆ zinc finger regulatory factor. The deletion of patL caused a drastic decrease in the expression of all pat genes, leading to an absence of patulin production. Pathogenicity studies performed on 13 apple varieties indicated that the PeΔpatL strain could still infect apples, but the intensity of symptoms was weaker compared with the wild‐type strain. A lower growth rate was observed in the PeΔpatL strain when this strain was grown on nine of the 13 apple varieties tested. In the complemented PeΔpatL:patL strain, the ability to grow normally in apple and the production of patulin were restored. Our results clearly demonstrate that patulin is not indispensable in the initiation of the disease, but acts as a cultivar‐dependent aggressiveness factor for P. expansum. This conclusion was strengthened by the fact that the addition of patulin to apple infected by the PeΔpatL mutant restored the normal fungal colonization in apple.     

Improved Adaptation to Cold-Shock, Stationary-Phase, and Freezing Stresses in Lactobacillus plantarum Overproducing Cold-Shock Proteins

We have investigated the effect of overproducing each of the three cold shock proteins (CspL, CspP, and CspC) in the mesophilic lactic acid bacterium Lactobacillus plantarum NC8. CspL overproduction transiently alleviated the reduction in growth rate triggered by exposing exponentially growing cells to cold shock (8°C), suggesting that CspL is involved in cold adaptation. The strain overproducing CspC resumed growth more rapidly when stationary-phase cultures were diluted into fresh medium, indicating a role in the adaptation and recovery of nutritionally deprived cells. Overproduction of CspP led to an enhanced capacity to survive freezing.     

Various Levels of Cross-Resistance to Bacillus sphaericus Strains in Culex pipiens (Diptera: Culicidae) Colonies Resistant to B. sphaericus Strain 2362

We studied the cross-resistance to three highly toxic Bacillus sphaericus strains, IAB-59 (serotype H6), IAB-881 (serotype H3), and IAB-872 (serotype H48), of four colonies of the Culex pipiens complex resistant to B. sphaericus 2362 and 1593, both of which are serotype H5a5b strains. Two field-selected highly resistant colonies originating from India (KOCHI, 17,000-fold resistance) and France (SPHAE, 23,000-fold resistance) and a highly resistant laboratory-selected colony from California (GeoR, 36,000-fold resistance) showed strong cross-resistance to strains IAB-881 and IAB-872 but significantly weaker cross-resistance to IAB-59 (3- to 43-fold resistance). In contrast, a laboratory-selected California colony with low-level resistance (JRMM-R, 5-fold resistance) displayed similar levels of resistance (5- to 10-fold) to all of the B. sphaericus strains tested. Thus, among the mosquitocidal strains of B. sphaericus we identified a strain, IAB-59, which was toxic to several Culex colonies that were highly resistant to commercial strains 2362 and 1593. Our analysis also indicated that strain IAB-59 may possess other larvicidal factors. These results could have important implications for the development of resistance management strategies for area-wide mosquito control programs based on the use of B. sphaericus preparations.     

Phylogenesis of Brain Glutamic Acid Decarboxylase from Vertebrates: Immunochemical Studies

Brain high-speed supernatants from various lower and higher vertebrates were subjected to sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, electroblot on nitrocellulose membranes, and immunolabelling using an anti-glutamic acid decarboxylase (anti-GAD) antiserum prepared from rat antigen. Rat brain extracts showed two distinct immunolabelled bands (MW 59,000 and 62,000 daltons). The molecular weight of the native enzyme was 120,000 daltons. The immunoblot pattern was not affected by a 3-h incubation of the homogenate. In the substantia nigra, the decrease in the immunolabelling of both bands corresponded very closely to the decrease of GAD activity following lesioning of the striato-nigral pathway. Moreover, experiments with preadsorbed antiserum showed that both subunits have common antigenic determinants. The immunolabelling was consistently more intense over the lightest band. The autoradiography of immunoprecipitated rat brain GAD, iodinated prior to electrophoresis, revealed two radiolabelled bands corresponding to the two immunolabelled ones. Their radioactivity was found in a one-to-five ratio which closely paralleled their respective immunolabelling intensity. Thus, the two subunits recognized by the antiserum are not present in stoichiometric proportions in the rat brain high-speed supernatant. These findings suggest the existence of two homodimeric GAD with common antigenic determinants which are present in different amounts. Immunoprecipitation curves of brain GAD from rat, mouse, rabbit, monkey, human, quail, frog, and trout were similar, with a less than 10-fold maximum shift in affinity for GAD. GAD immunoblots from the various higher vertebrates showed a pattern similar to that obtained in rat.(ABSTRACT TRUNCATED AT 250 WORDS)