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.

Mode of action of Bacillus thuringiensis Cry and Cyt toxins and their potential for insect control.

Insecticidal activity of Bacillus thuringiensis crystal proteins

Publisher Summary This chapter provides an overview of the biology of Bacillus thuringiensis ( Bt ). The chapter examines how the recently solved X-ray crystal structure of one Bt toxin allows to model the mode of action of a whole family of related protein toxins, and how a knowledge of the physiology of the insect targets of Bt toxins is needed for a better understanding of the toxic mechanism. Bacillus thuringiensis ( Bt ), a family of bacteria which make insecticidal proteins, accounts for 90–95% of the insect biocontrol market. This chapter illustrates that Bt is the name given to a family of bacteria found throughout the world. Paradoxically, CryIIIA, the only Bt toxin whose three-dimensional structure has been solved, kills very small insects, and its insolubility at neutral pH makes it difficult to assay in vitro . The crystal structure of CryIIIA permits site-directed mutagenesis and segment swapping experiments to be designed in a rational manner in order to identify the functional domains of the toxins. This chapter explores one attractive prospect that can be the replacement of the specificity domain with a binding domain directed to a target of choice, opening up the possibility of “designer” pesticides or a new class of immunotoxins. Characterization of toxin receptors and investigation of the mechanism of toxin synergism may assist in strategies for resistance management, a vital concern if Bt is to maintain its important position as the most extensively used biological insecticide.

Mechanism of Action of Bacillus thuringiensis Insecticidal δ-Endotoxins

Summary: Bacillus thuringiensis var. israelensis crystal proteins were purified by FPLC on a Mono Q column to yield 130, 65, 28, 53, 30-35 and 25 kDa proteins. All the purified proteins killed Aedes aegypti larvae after citrate precipitation, but the 65 kDa protein was the most toxic. A precipitated mixture of 27 and 130 kDa proteins was almost as toxic as solubilized crystals. In assays against a range of insect cell lines, the activated form (25 kDa) of the 27 kDa protein was generally cytotoxic with the lowest LC50 values in vitro. By contrast, the activated forms of the 130 kDa and 65 kDa protoxins (53 kDa and 30-35 kDa proteins, respectively) were much more specific than the 25 kDa protein in their action on dipteran cells, and each showed a unique toxicity profile which, in the case of the 130 kDa preparation, was restricted to Anopheles and Culex cell lines.

Comparative toxicity of Bacillus thuringiensis var. israelensis crystal proteins in vivo and in vitro.

A novel antibiotic-producing Bacillus sp. is provided that exhibits antifungal activity only on certain specific plant pathogens and no antibacterial activity is provided by this invention as well as a biologically pure culture of a strain having all the identifying characteristics of this strain. Also provided is a method of treating or protecting plants, fruit and roots from fungal infections by applying an effective amount of these strains, supernatants produced by these strains or a metabolite isolated from these strains.

Strain of bacillus for controlling plant diseases

The Bacillus thuringiensis subsp. israelensis (B.t.i.) parasporal body is a gut poison, and the midgut epithelium of affected larvae is considered to be its initial site of action (de Barjac 1978). In B.t.i. -treated mosquito larvae, midgut epithelial cells swell and burst, causing severe damage to the gut wall (de Barjac 1978; Charles and de Barjac 1983; Lahkim-Tsror et al. 1983). The general characteristics of poisoning of B.t.i. -treated mosquito larvae (4 µg/ml) are cessation of feeding within one hour, reduced activity by two hours, extreme sluggishness by four hours, and general paralysis by six hours. Singh, Schouest, and Gill (1986) showed that the effect on the posterior midgut ultrastructure was detected as early as one hour, when the epithelial striated border was damaged. This was followed by swelling of epithelial organelles. Midgut circular and longitudinal muscles were also damaged, as indicated by their swelling and separation from the basement lamina. Six hours after B.t.i. treatment the midgut wall was severely ruptured, with the peritrophic membrane and basement lamina broken. Of these lesions, disruption of microvilli and epithelial swelling in the midgut coincide with cessation of feeding. The sluggish behavior and paralysis of insects only occurred in advanced stages of parasporal body poisoning.

Mechanism of Action of Bacillus thuringiensis israelensis Parasporal Body

The present invention relates to a newly isolated Bacillus thuringiensis strain which exhibits insecticidal activity. The supernatant of cultures of this novel strain is also an effective insecticidal agents. Also included in the invention are the novel B. thuringiensis isolate, its supernatant and a solvent extract of the supernatant which are specifically active against corn rootworm but not against beet armyworm, nematodes or flies. These strains and supernatants may be used to treat plants infected with susceptible organisms.

Bacillus thuringiensis strain and metabolite which are active against corn rootworm

The present invention provides a novel Bacillus thuringiensis strain that exhibits broad antifungal and antibacterial activity. The invention also provides the use of the Bacillus thuringiensis strain or the antibiotic produced by the strain for control of a broad range of fungal and bacterial plant pathogens.

Chris N. Chilcott

Papers

Comparative toxicity of Bacillus thuringiensis var. israelensis crystal proteins in vivo and in vitro.

Strain of bacillus for controlling plant diseases

Mechanism of Action of Bacillus thuringiensis israelensis Parasporal Body

Bacillus thuringiensis strain and metabolite which are active against corn rootworm

A novel strain of bacillus for controlling plant disease