Search results for "MIDGUT"

Insecticidal spectrum and mode of action of the Bacillus thuringiensis Vip3Ca insecticidal protein.

2016

The Vip3Ca protein, discovered in a screening of Spanish collections of Bacillus thuringiensis, was known to be toxic to Chrysodeixis chalcites, Mamestra brassicae and Trichoplusia ni. In the present study, its activity has been tested with additional insect species and we found that Cydia pomonella is moderately susceptible to this protein. Vip3Ca (of approximately 90 kDa) was processed to an approximately 70 kDa protein when incubated with midgut juice in all tested species. The kinetics of proteolysis correlated with the susceptibility of the insect species to Vip3Ca. The activation was faster to slower in the following order: M. brassicae (susceptible), Spodoptera littoralis (moderately…

Susceptibility, mechanisms of response and resistance to Bacillus thuringiensis toxins in Spodoptera spp.

2016

Bioinsecticides based on Bacillus thuringiensis have long been used as an alternative to synthetic insecticides to control insect pests. In this review, we focus on insects of the genus Spodoptera, including relevant polyphagous species that are primary and secondary pests of many crops, and how B. thuringiensis toxins can be used for Spodoptera spp. pest management. We summarize the main findings related to susceptibility, midgut binding specificity, mechanisms of response and resistance of this insect genus to B. thuringiensis toxins.

Artefactual band patterns by SDS-PAGE of the Vip3Af protein in the presence of proteases mask the extremely high stability of this protein.

2018

Abstract Vip3 proteins are secretable proteins from Bacillus thuringiensis with important characteristics for the microbiological control of agricultural pests. The exact details of their mode of action are yet to be disclosed and the crystallographic structure is still unknown. Vip3 proteins are expressed as protoxins that have to be activated by the insect gut proteases. A previous study on the peptidase processing of Vip3Aa revealed that the protoxin produced artefactual band patterns by SDS-PAGE due to the differential stability of this protein and the peptidases to SDS and heating (Bel et al., 2017 Toxins 9:131). To determine whether this phenomenon also applies to other Vip3A proteins…

Analysis of cross-resistance to Vip3 proteins in eight insect colonies, from four insect species, selected for resistance to Bacillus thuringiensis i…

2018

Abstract Bacillus thuringiensis Vip3 proteins are synthesized and secreted during the vegetative growth phase. They are activated by gut proteases, recognize and bind to midgut receptors, form pores and lyse cells. We tested the susceptibility to Vip3Aa and Vip3Ca of Cry1A-, Cry2A-, Dipel- and Vip3-resistant insect colonies from different species to determine whether resistance to other insecticidal proteins confers cross-resistance to Vip3 proteins. As expected, the colonies resistant to Cry1A proteins, Dipel (Helicoverpa armigera, Trichoplusia ni, Ostrinia furnacalis and Plodia interpunctella) or Cry2Ab (H. armigera and T. ni) were not cross-resistant to Vip3 proteins. In contrast, H. arm…

Bacterial Vegetative Insecticidal Proteins (Vip) from Entomopathogenic Bacteria

2016

SUMMARY Entomopathogenic bacteria produce insecticidal proteins that accumulate in inclusion bodies or parasporal crystals (such as the Cry and Cyt proteins) as well as insecticidal proteins that are secreted into the culture medium. Among the latter are the Vip proteins, which are divided into four families according to their amino acid identity. The Vip1 and Vip2 proteins act as binary toxins and are toxic to some members of the Coleoptera and Hemiptera. The Vip1 component is thought to bind to receptors in the membrane of the insect midgut, and the Vip2 component enters the cell, where it displays its ADP-ribosyltransferase activity against actin, preventing microfilament formation. Vip3…

Acute appendicitis and situs viscerum inversus: radiological and surgical approach—a systematic review

2023

Abstract Introduction Acute appendicitis is one of the most frequent intra-abdominal diseases requiring emergency surgical consult and treatment. The diagnosis of this condition is based on clinical features and radiologic findings. One-third of patients with acute appendicitis present unusual symptoms. There are several circumstances that may cause misdiagnosis and unclear prognostic prediction. Among these, situs viscerum inversus totalis and midgut malrotation can be challenging scenarios, leading to a delay in treatment, especially when these conditions are unknown. We decided to carry on a systematic review of published cases of acute appendicitis in the context of anatomical anomalies…

Effect of Bacillus thuringiensis toxins on the midgut of the nun moth Lymantria monacha.

2000

Three steps of the proposed mode of action of Bacillus thuringiensis toxins have been studied in Lymantria monacha. We demonstrated that only the toxins that caused typical pathological changes in midgut epithelial cells and bound to the midgut brush border membrane were able to drastically reduce the midgut transepithelial voltage of the nun moth.

Comparison of Different Methodologies for Binding Assays of Bacillus thuringiensis Toxins to Membrane Vesicles from Insect Midguts

2002

Occurrence of a common binding site in Mamestra brassicae, Phthorimaea operculella, and Spodoptera exigua for the insecticidal crystal proteins CryIA…

1997

Specific binding to midgut membrane proteins is required for the toxicity of insecticidal crystal proteins (ICP) from Bacillus thuringiensis. A direct relationship between toxicity and binding has been proposed. It has been hypothesized that sharing of a single receptor by more than one ICP could lead to the occurrence of multiple resistance in the event of an alteration in the common receptor. Binding of CryIA(a), CryIA(b) and CryIA(c), three structurally related ICPs, has been studied in Phthorimaea operculella, Mamestra brassicae and, Spodoptera exigua using brush border membrane vesicles (BBMV) from the midgut tissue. Using iodinated CryIA(b), the three insects showed similar results: o…

Resistance to the Bacillus thuringiensis bioinsecticide in a field population of Plutella xylostella is due to a change in a midgut membrane receptor.

1991

The biochemical mechanism for resistance to Bacillus thuringiensis crystal proteins was studied in a field population of diamondback moths (Plutella xylostella) with a reduced susceptibility to the bioinsecticidal spray. The toxicity and binding characteristics of three crystal proteins [CryIA(b), CryIB, and CryIC] were compared between the field population and a laboratory strain. The field population proved resistant (greater than 200-fold compared with the laboratory strain) to CryIA(b), one of the crystal proteins in the insecticidal formulation. Binding studies showed that the two strains differ in a membrane receptor that recognizes CryIA(b). This crystal protein did not bind to the b…