During the past decade the pesticidal bacterium Bacillus thuringiensis has been the subject of intensive research. These efforts have yielded considerable data about the complex relationships between the structure, mechanism of action, and genetics of the organism’s pesticidal crystal proteins, and a coherent picture of these relationships is beginning to emerge. Other studies have focused on the ecological role of the B. thuringiensis crystal proteins, their performance in agricultural and other natural settings, and the evolution of resistance mechanisms in target pests. Armed with this knowledge base and with the tools of modern biotechnology, researchers are now reporting promising results in engineering more-useful toxins and formulations, in creating transgenic plants that express pesticidal activity, and in constructing integrated management strategies to insure that these products are utilized with maximum efficiency and benefit.

Bacillus thuringiensis and Its Pesticidal Crystal Proteins

Insecticidal crystal proteins of Bacillus thuringiensis.

characterized by its ability to produce crystalline inclusions during spor-ulation. TIhese inclusions consist of proteins exhibiting a highly specific insecticidal activity (reviewed in references 4 and 97). Many B. thuriuigiensis strains with different insect host spectra have been identified (9). TIhey ar-e classified into different serotypes or subspecies based on their flagellar antigens. Most strains are active against larvae of certain members of the Lepidoptera, but some show toxicity against dipterian (reviewed in refer-ence 22) or coleopteran (53) species. For several cryst.al-producing strains.

Insecticidal crystal proteins of Bacilllus thuringiensis

General Aspects.- Systematics.- Biology of Mosquitoes.- Medical Importance of Mosquitoes.- Mosquito Research Techniques.- Morphology of Mosquitoes.- Identification Keys Morphology Ecology and Distribution of European Species.- Key to Female Mosquitoes.- Key to Male Mosquitoes.- Key to Mosquito Fourth Instar Larvae.- Subfamily Anophelinae.- Subfamily Culicinae.- Identification Keys, Morphology, Ecology and Distribution of Important Vector and Nuisance Species - Worldwide.- Africa.- Asia.- Australia.- Central and South America.- North America.- Control of Mosquitoes.- Biological Control.- Environmental Management of Mosquitoes.- Chemical Control.- Physical Control.- Genetic Control of Mosquitoes.- Personal Protection.- Implementation and Integration of Mosquito Control Measures.

Mosquitoes and their Control

Insect digestive enzymes: properties, compartmentalization and function

Preparation and partial characterization of amino acid transporting brush border membrane vesicles from the larval midgut of the cabbage butterfly (Pieris brassicae)

K+ transport by the epithelia of midgut, salivary glands, Malpighian tubules, sensory sensilla, possibly rectum, and other organs of certain insects appears to use a unique K+ ATPase. Ouabain inhibition of transport-related events has not been demonstrated in these epithelia. The K+ pump is unlike the Na-K;ump but resembles the H;ump of phosphorylating membranes in its transport orientation, efficient thermodynamics, speculated two K+ per one MgATP2- stoichiometry, electrogenicity, and structure. Older electrochemical, tracer flux, and conductance evidence suggested that the K+ pump was on the apical plasma membrane of transporting cells in these epithelia. New X-ray microanalytical studies (XMA), reveal that the K+ concentration in all cells is more than 100 mM. Together with new microelectrode data these XMA results confirm the apical K+ pump location, resolve the K+ transport sport route, and suggest that the goblet cell cavity facilitates the generation of a large apical PD which may be used in nutrient absorption and pH regulation. K+ portasomes, which resemble F1-Fo ATPase particles, stud these K+ transporting apical membranes and are though to be the unit of active K+ transport. We have suggested a K+ transport mechanism in which two cations (2K+) are abandoned in an isolated domain of the portasomes during ATP2-hydrolysis and are repelled to the opposite membrane side via a K+ channel. Small peptides hydrolysed from the delta-endotoxin of Bacillus thuringiensis inhibit the K+ transport and may be useful as K+ pump inhibitors, apical membrane probes and insecticides. Goblet cell apical membrane fragments (GCAM) as well as fragments from columnar cell apical membrane (CCAM), lateral membrane (LM) and basal membranes (BM) were isolated as clean fractions using ultrasound, aspiration, and both differential and density gradient centrifugation; purification was monitored by electron microscopy. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS PAGE) reveals that GCAM, CCAM, LM and BM have very different protein compositions. Preliminary enzymology is consistent with the K+ ATPase being on the apical plasma membrane of the goblet cells of midgut and enveloping cells of sensilla.

Potassium ion transport ATPase in insect epithelia

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1016/0014-5793%2886%2980814-6

Bacillus thuringiensis toxin inhibits K+-gradient-dependent amino acid transport across the brush border membrane of Pieris brassicae midgut cells

After incubation at pH 10 or higher, Bacillus thuringiensis spores and endotoxin, at concentrations above 0.1 IU/ml, affected transport parameters in the isolated midgut of Manduca sexta larvae. (Toxic activity was lost during roughly 1 week at pH 11.) About 60% of the short-circuit current was inhibited, and the remainder was reversibly inhibited by anoxia. Electrical resistance was reduced by about 55% and oxygen uptake stimulated by about 30%. Influx of potassium from blood-side to lumen-side ('active' flux) was unaffected but flux in the reverse direction was nearly tripled. These results suggest that hydrolysis of the toxin yields an inhibitor of potassium transport, presumably a polypeptide. It is argued that inhibition is not primarily by uncoupling of oxidative phosphorylation, but instead by interference with an active depression of the efflux of potassium from lumen-side to blood-side.

Michael G. Wolfersberger

Papers

Preparation and partial characterization of amino acid transporting brush border membrane vesicles from the larval midgut of the cabbage butterfly (Pieris brassicae)

Potassium ion transport ATPase in insect epithelia

Bacillus thuringiensis toxin inhibits K+-gradient-dependent amino acid transport across the brush border membrane of Pieris brassicae midgut cells

Mechanism of inhibition of active potassium transport in isolated midgut of Manduca sexta by Bacillus thuringiensis endotoxin.

Cation-stimulated ATPase activity in purified plasma membranes from tobacco hornworm midgut.