Adaptation of Bacillus thuringiensis to Plant Colonization Affects Differentiation and Toxicity (original) (raw)
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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...
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.
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.
How Bacillus thuringiensis has evolved specific toxins to colonize the insect world
Trends in Genetics, 2001
Spore coat protein synergizes Bacillus thuringiensis crystal toxicity for the Indianmeal moth (Plodia interpunctella). Curr. Microbiol. 36, 278-282 c Schnepf, E. et al. (1998) Bacillus thuringiensis and its pesticidal crystal proteins. Microbiol. Mol. Biol. Rev. 62, 775-806 Box 1. The armory of an insect pathogen
Relocating expression of vegetative insecticidal protein into mother cell of Bacillus thuringiensis
Biochemical and Biophysical Research Communications, 2003
Vegetative insecticidal protein (VIP) is a class of insecticidal proteins produced by some strains of Bacillus thuringiensis during the vegetative stage of their growth. Unlike d-endotoxins which are produced as parasporal inclusion bodies within the cell during sporulation, VIP is secreted into the culture medium. Here we report the relocation of the expression of VIP into the mother cell compartment in a manner similar to well-characterized Cry proteins. Relocation of VIP is directed to mother cell by placing its synthesis under sporulation-dependent promoters, BtI and BtII. The insertion of cry preferred transcription termination sequence at the 3 0 region and a STAB-SD sequence at the 5 0 region of the gene provided stability to the vip transcript and enhanced its yield. The demonstrated expression of VIP within the cells in the form of inclusion bodies would facilitate development of a suitable formulation for the application of this class of insecticidal proteins in the field.
A new Bacillus thuringiensis protein for Western corn rootworm control
PLOS ONE, 2020
The Western corn rootworm (WCR) Diabrotica virgifera virgifera LeConte is one of the most economically important insect pests in North America. Since 2003, transgenic maize expressing WCR-active proteins from Bacillus thuringiensis (Bt) have been widely adopted as the main approach to controlling WCR in the U.S. However, the emergence of field resistance to the Bt proteins in current commercial products has been documented in recent years, highlighting the need to develop additional tools for controlling this devasting pest. Here we report the discovery of Vpb4Da2 (initially assigned as Vip4Da2), a new insecticidal protein highly selective against WCR, through high-throughput genome sequencing of a Bt strain sourced from grain dust samples collected in the eastern and central regions of the US. Vpb4Da2 contains a sequence and domain signature distinct from families of other WCR-active proteins. Under field conditions, transgenic maize expressing Vpb4Da2 demonstrates commercial-level...
Molecular Ecology, 2021
The intensification of agriculture has resulted in an increased reliance on large scale pest control, both chemical and biological. Transgenic crops expressing insecticidal toxins have been successful at managing pests but are not without limitations, as numerous species have evolved resistance (Tabashnik & Carrière, 2017). Studies aimed at characterizing resistance have largely focused on target-site or metabolic mutations in insects (Pardo-Lopez et al., 2013). However, microbial communities associated with insects can influence host fitness and susceptibility to pesticides, but are often overlooked when characterizing resistance (Douglas, 2018; Gressel, 2018).
Annals of Microbiology, 2007
The entomopathogenic bacteriumBacillus thuringiensis is widely used for the control of many agricultural insect pests and vectors of human diseases. Several studies reported also on its antibacterial and antifungal activities. However, to our knowledge there were no studies dealing with its capacity to act as a plant growth promoting bacterium. This review surveys the potential ofB. thuringiensis as a polyvalent biocontrol agent, a biostimulator and biofertiliser bacterium that could promote the plant growth. Also, discussed is the safety ofB. thuringiensis as a bacterium phylogenetically related toBacillus cereus the opportunistic human pathogen andBacillus anthracis, the etiological agent of anthrax.
Applied and Environmental Microbiology, 2004
Bacillus thuringiensis vegetative cells are known to be highly pathogenic when injected into the hemocoel of susceptible insect larvae. This pathogenicity is due to the capacity of B. thuringiensis to cause septicemia in the host. We screened a B. thuringiensis mini-Tn10 insertion library for loss of virulence against Bombyx mori larvae on injection into the hemocoel. Three clones with attenuated virulence were isolated, corresponding to two different mini-Tn10 insertions mapping to the yqgB/yqfZ locus. Single disruptions of the yqgB and yqfZ genes did not affect virulence against B. mori. In contrast, the inactivation of both genes simultaneously reproduced the effect of the mini-Tn10 insertion and resulted in a significant delay to infection. The double ⌬yqgB ⌬yqfZ mutant was also nonmotile, and its growth was affected at 25°C. We analyzed lacZ transcriptional fusions and detected promoter activity upstream from yqgB at 25 and 37°C. Overall, our findings suggest that the yqgB and yqfZ genes encode adaptive factors that may act in synergy, enabling the bacteria to cope with the physical environment in vivo, facilitating colonization of the host.
Frontiers in Microbiology
Using the model host/pathogen pair Galleria mellonella/Bacillus thuringiensis, we have shown that these bacteria could kill their insect host, survive in its cadaver and form spores by sequentially activating virulence, necrotrophism and sporulation genes. However, the population isolated from the cadavers was heterogeneous, including non-sporulating cells in an unknown physiological state. To characterize these bacteria, we used a transcriptional fusion between the promoter of a gene expressed during early exponential growth (abrB) and a reporter gene encoding a destabilized version of GFP, in combination with a fluorescent reporter of the necrotrophic state. The composition of the bacterial population during infection was then analyzed by flow cytometry. We showed that the PabrB promoter was activated in the population that had turned on the necrotrophic reporter, suggesting a re-entry into vegetative growth. Strikingly, the cells that did not go through the necrotrophic state did not activate the PabrB promoter and appear as a dormant subpopulation. We propose a new model describing the B. thuringiensis cell types during infection.