Two new Brazilian isolates of Bacillus thuringiensis toxic to Anticarsia gemmatalis (Lepidoptera: Noctuidae)

Importance of Cry Proteins in Biotechnology: Initially a Bioinsecticide, Now a Vaccine Adjuvant

A hallmark of Bacillus thuringiensis bacteria is the formation of one or more parasporal crystal (Cry) proteins during sporulation. The toxicity of these proteins is highly specific to insect larvae, exerting lethal effects in different insect species but not in humans or other mammals. The aim of this review is to summarize previous findings on Bacillus thuringiensis, including the characteristics of the bacterium, its subsequent contribution to biotechnology as a bioinsecticide due to the presence of Cry proteins, and its potential application as an adjuvant. In several studies, Cry proteins have been administered together with specific antigens to immunize experimental animal models. The results have shown that these proteins can enhance immunogenicity by generating an adequate immune response capable of protecting the model against an experimental infectious challenge, whereas protection is decreased when the specific antigen is administered without the Cry protein. Therefore, based on previous results and the structural homology between Cry proteins, these molecules have arisen as potential adjuvants in the development of vaccines for both animals and humans. Finally, a model of the interaction of Cry proteins with different components of the immune response is proposed.

Mode of Action and Specificity of Bacillus thuringiensis Toxins in the Control of Caterpillars and Stink Bugs in Soybean Culture

The bacterium Bacillus thuringiensis (Bt) produces delta-endotoxins that possess toxic properties and can be used as biopesticides, as well as a source of genes for the construction of transgenic plants resistant to insects. In Brazil, the introduction of Bt soybean with insecticidal properties to the velvetbean caterpillar, the main insect pest of soybean, has been seen a promising tool in the management of these agroecosystems. However, the increase in stink bug populations in this culture, in various regions of the country, which are not susceptible to the existing genetically modified plants, requires application of chemicals that damage the environment. Little is known about the actual toxicity of Bt to Hemiptera, since these insects present sucking mouthparts, which hamper toxicity assays with artificial diets containing toxins of this bacterium. In recent studies of cytotoxicity with the gut of different hemipterans, susceptibility in the mechanism of action of delta-endotoxins has been demonstrated, which can generate promising subsidies for the control of these insect pests in soybean. This paper aims to review the studies related to the selection, application and mode of action of Bt in the biological control of the major pest of soybean, Anticarsia gemmatalis, and an analysis of advances in research on the use of Bt for control hemipterans.

Identification of cultivable bacteria in the intestinal tract of Bactrocera dorsalis from three different populations and determination of their attractive potential

BACKGROUND

This study aimed to identify the cultivable bacteria inhabiting the intestinal tract of adult oriental fruit flies (Bactrocera dorsalis) from laboratory-reared, laboratory sterile sugar-reared, and field-collected populations, and to evaluate the attractiveness of the metabolites produced by the above bacteria to their hosts.

RESULTS

Fifteen bacterial isolates chosen from the three populations were determined at species level. These 15 strains were cultured and the attractiveness of the whole Luria-Bertani broth, filtered and autoclaved supernatants to B. dorsalis adults was determined using bioassays. The bioassays showed that all bacterial strains were significantly more attractive to B. dorsalis adults than the media-only control. Among them, Bacillus cereus, Enterococcus faecalis, Enterobacter cloacae and Citrobacter freundii were the most attractive bacteria. Furthermore, results of a subsequent field test showed that the six bacterial strains were significantly more attractive than the control, with B. cereus and E. faecalis attracting significantly more flies.

CONCLUSIONS

A cultivable bacterial community composed of Enterobacteriaceae, Enterococcaceae, and Bacillaceae was identified in the intestinal tract of B. dorsalis. Metabolites from B. cereus attracted the greatest number of B. dorsalis adults in the laboratory and field. These results provide useful information for the development of bacterial biocontrol agents or implementation as an insecticide.

Receptors and Lethal Effect of Bacillus thuringiensis Insecticidal Crystal Proteins to the Anticarsia gemmatalis (Lepidoptera, Noctuidae)

Bioassays with insecticidal crystal proteins (ICPs) from Bacillus thuringiensis have demonstrated that Cry1Aa, Cry1Ac, and Cry1Ba are the most active toxins on larvae of the Anticarsia gemmatalis. The toxins Cry1Da and Cry1Ea are less toxic, and toxins Cry2Aa are not active. Binding of these ICPs to midgut sections of the A. gemmatalis larvae was studied using streptavidin-mediated detection. The observed staining patterns showed that Cry1Aa and Cry1Ac bound to the brush border throughout the whole length of the midgut. However, the binding sites of Cry1Ba were not evenly distributed in the midgut microvilli. The in vivo assays against larvae of 2nd instar A. gemmatalis confirmed the results from the in vitro binding studies. These binding data correspond well with the bioassay results, demonstrating a correlation between receptors binding and toxicity of the tested ICPs in this insect.