The Insecticidal Proteins of Bacillus thuringiensis (original) (raw)
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Bacillus thuringiensis Toxins: An Overview of Their Biocidal Activity
Toxins, 2014
Bacillus thuringiensis (Bt) is a Gram positive, spore-forming bacterium that synthesizes parasporal crystalline inclusions containing Cry and Cyt proteins, some of which are toxic against a wide range of insect orders, nematodes and human-cancer cells. These toxins have been successfully used as bioinsecticides against caterpillars, beetles, and flies, including mosquitoes and blackflies. Bt also synthesizes insecticidal proteins during the vegetative growth phase, which are subsequently secreted into the growth medium. These proteins are commonly known as vegetative insecticidal proteins (Vips) and hold insecticidal activity against lepidopteran, coleopteran and some homopteran pests. A less well characterized secretory protein with no amino acid similarity to Vip proteins has shown insecticidal activity against coleopteran pests and is termed Sip (secreted insecticidal protein). Bin-like and ETX_MTX2-family proteins (Pfam PF03318), which share amino acid similarities with mosquitocidal binary (Bin) and Mtx2 toxins, respectively, from Lysinibacillus sphaericus, are also produced by some Bt strains. In addition, vast numbers of Bt isolates naturally present in the soil and the phylloplane also synthesize
Purification and characterization of Bacillus thuringiensis vegetative insecticidal toxin protein(s)
Significance and Impact of the Study: Insecticidal activity of Bacillus thuringiensis subsp. aegypti was determined, and its vegetative insecticidal protein was subjected to FPLC for protein purification. This work contributes to improve understanding the different toxins secreted during vegetative growth of Bt. Moreover, the N-terminal amino acid sequences of 88-kDa protein was only 92% identical to that of vip3A, and for 44 kDa was 92% identical with Cry35a, suggesting that we might have identified a new genes. Finally, we have proven these proteins to be novel insecticidal agents that may complement the use of known insecticidal proteins derived from Bacillus.
Bacillus thuringiensis : from biodiversity to biotechnology
Journal of Industrial Microbiology & Biotechnology, 1997
is a Gram-positive bacterium, widely used in agriculture as a biological pesticide. The biocidal activity mainly resides in a parasporal protein inclusion body, or crystal. The inclusion is composed of one or more types of δ-endotoxins (Cry and Cyt proteins). Cry proteins are selectively toxic to different species from several invertebrate phyla: arthropods (mainly insects), nematodes, flatworms and protozoa. The mode of action of the insecticidal proteins is still a matter of investigation; generally, the active toxin is supposed to bind specific membrane receptors on the insect midgut brush-border epithelium, leading to intestinal cell lysis and subsequent insect death by starvation or septicemia. The toxin-encoding cry genes have been extensively studied and expressed in a large number of prokaryotic and eukaryotic organisms. The expression of such genes in transgenic plants has provided a powerful alternative for crop protection.
Current Microbiology, 2003
Little is known about the occurrence and linkage between secreted insecticidal virulence factors in natural populations of Bacillus thuringiensis (Bt). We carried out a survey of 392 Bt strains isolated from various samples originating from 31 countries. The toxicity profile of the culture supernatants of these strains was determined individually against Anthonomus grandis (Coleoptera) and Spodoptera littoralis (Lepidoptera). We analyzed -exotoxin I production and searched for the genes encoding Vip1-2, Vip3, and Cry1I toxins in 125 of these strains. Our results showed that these insecticidal toxins were widespread in Bt but that their distribution was nonrandom, with significant linkage observed between vip3 and cry1I and between vip1-2 and -exotoxin I. Strains producing significant amounts of -exotoxin I were more frequently isolated from invertebrate samples than from dust, water, soil, or plant samples.
Evolution of Bacillus thuringiensis Cry toxins insecticidal activity
Microbial Biotechnology, 2013
Insecticidal Cry proteins produced by Bacillus thuringiensis are use worldwide in transgenic crops for efficient pest control. Among the family of Cry toxins, the three domain Cry family is the better characterized regarding their natural evolution leading to a large number of Cry proteins with similar structure, mode of action but different insect specificity. Also, this group is the better characterized regarding the study of their mode of action and the molecular basis of insect specificity. In this review we discuss how Cry toxins have evolved insect specificity in nature and analyse several cases of improvement of Cry toxin action by genetic engineering, some of these examples are currently used in transgenic crops. We believe that the success in the improvement of insecticidal activity by genetic evolution of Cry toxins will depend on the knowledge of the rate-limiting steps of Cry toxicity in different insect pests, the mapping of the specificity binding regions in the Cry toxins, as well as the improvement of mutagenesis strategies and selection procedures.
Continuous evolution of Bacillus thuringiensis toxins overcomes insect resistance
2016
The expression of insecticidal proteins from B. thuringiensis (Bt toxins) in crops has proved to be a valuable strategy for agricultural pest management1. Bt-toxin-producing crops have been widely adopted in agriculture with substantial economic and environmental benefits2, and have increased global agricultural productivity by an estimated US$78 billion from 1996 to 2013 (ref. 3). Unfortunately, Bt toxin resistance has evolved among insect pests and threatens the continued success of this strategy for pest control4. While resistance management strategies have been developed, including the use of multiple Bt toxins and preserving susceptible alleles in insect populations, the evolution of insect resistance to Bt toxins remains the most serious current threat to sustaining the gains offered by transgenic crops4. Bt toxins interact with protein receptors on the surface of insect midgut cells, leading to pore formation in the cell membrane and cell death5. Bt toxin resistance is common...
Understanding the impact of Bacillus thuringiensis proteins on non-target organisms
International Journal of Scientific Research in Biological Sciences
Bacillus thuringiensis (Bt) is a spore-forming, gram-positive, aerobic, rod-shaped bacterium. During sporulation, Bt produces proteinaceous crystals called Cry proteins that are lethal to many insects' species, so are commonly used as biological pesticide. Transgenic Bt crops are genetically altered to express insecticidal toxins that cause fatality of a number of general agricultural pests. The insecticidal toxins formed by Bt crops possess narrow range of toxicity and therefore less non-target impacts as compared to conventional insecticides. A decrease in the amount and regularity of insecticide applications are financially advantageous. In numerous regions of the world, insecticide inputs have been significantly reduced because of Bt. The use of Bt crop technology might help in worldwide food security by escalating the amount and steadiness of crop yields. Though impact of Bt toxin on non-targeted organism is a serious issue yet no conclusion could still be drawn from several studies. This review summarizes the benefits of Bt crops including the impact on non-targeted organisms and Bt toxins having potential risks with respect to the environment.
Molecular Approaches to Improve the Insecticidal Activity of Bacillus thuringiensis Cry Toxins
Toxins, 2014
Bacillus thuringiensis (Bt) is a gram-positive spore-forming soil bacterium that is distributed worldwide. Originally recognized as a pathogen of the silkworm, several strains were found on epizootic events in insect pests. In the 1960s, Bt began to be successfully used to control insect pests in agriculture, particularly because of its specificity, which reflects directly on their lack of cytotoxicity to human health, non-target organisms and the environment. Since the introduction of transgenic plants expressing Bt genes in the mid-1980s, numerous methodologies have been used to search for and improve toxins derived from native Bt strains. These improvements directly influence the increase in productivity and the decreased use of chemical insecticides on OPEN ACCESS Toxins 2014, 6 2394 Bt-crops. Recently, DNA shuffling and in silico evaluations are emerging as promising tools for the development and exploration of mutant Bt toxins with enhanced activity against target insect pests. In this report, we describe natural and in vitro evolution of Cry toxins, as well as their relevance in the mechanism of action for insect control. Moreover, the use of DNA shuffling to improve two Bt toxins will be discussed together with in silico analyses of the generated mutations to evaluate their potential effect on protein structure and cytotoxicity.