Bacillus thuringiensis is the most widely used bacterium as a bioinsecticide worldwide. This bacterium produces, during its period of sporulation, parasporal inclusions Crystal (Cry) and Cytolytic (Cyt) toxins, also known as δ-endotoxins, that are specifically toxic to agriculturally and medicinally important insect pests of several orders.
Nevertheless, the vast majority of these parasporal inclusions are not insecticides and may be related to other biological activities, such as the group of proteins called parasporins that have preferential cytotoxicity against mammalian cancer cells and are not toxic to normal cells.
During its vegetative growth phase, B. thuringiensis produces other insecticidal proteins known as vegetative insecticidal proteins (Vip) and the secreted insecticidal proteins (Sip). These proteins are toxic to insects of the orders Lepidoptera, Hemiptera and Coleoptera. Additionally, B. thuringiensis, visualized as a multifaceted microbial factory for the production of several other metabolites, can also synthesize chitinases.
In B. thuringiensis, the chitinases (EC 3.2.2.14) belong to the family 18 of glycosyl hydrolases (GH18), characterized for cleaving of β-1,4 linkage of N-acetyl glucosamine present in chitin chains. Like the midgut in insects is usually lined with a peritrophic membrane, composed of chitin and proteins the chitinolytic activity of B. thuringiensis has been suggested by perforating the peritrophic membrane barrier in the larval midgut, increase accessibility of the toxins to the epithelium such as Cry, Cyt and VIP toxins.
Author(s) Details:
Maria Cleoneide da Silva
Entomopathogenic Bacteria and Molecular Markers Laboratory, Maranhão State University (UEMA), Campus Caxias, Caxias, MA, Brazil.
Jeverson Renato Moraes Brito
Entomopathogenic Bacteria and Molecular Markers Laboratory, Maranhão State University (UEMA), Campus Caxias, Caxias, MA, Brazil.
Emanuelle Cristine Pereira de Sousa
Entomopathogenic Bacteria and Molecular Markers Laboratory, Maranhão State University (UEMA), Campus Caxias, Caxias, MA, Brazil.
Dalton Kaynnan de Prado Costa
Complex Genetics and Molecular Biology Laboratory, Maranhão State University (UEMA), Campus Caxias, Caxias, MA, Brazil.
Alessandra Maria Silva Vidigal
Complex Genetics and Molecular Biology Laboratory, Maranhão State University (UEMA), Campus Caxias, Caxias, MA, Brazil.
Recent Global Research Developments in B. thuringiensis in Cerrado soils: Toxicity to Aedes
In a study conducted in the Brazilian state of Maranhão, researchers investigated the potential of B. thuringiensis isolates obtained from Cerrado soils for the biological control of Aedes aegypti larvae1.
Isolate Identification:
- The B. thuringiensis colonies were obtained from soil samples, and their identification was based on morphological characteristics.
- Overall, 12 out of 300 isolates (4.0%) showed larvicidal activity against third-instar A. aegypti larvae.
- Notably, the isolates BtMA-104, BtMA-401, and BtMA-560 caused 100% mortality.
Virulence and Toxin Genes:
- The BtMA-401 isolate was the most virulent, with the lowest median lethal concentration (LC50) of 0.004 × 10^7 spores/mL.
- Protein profiles of certain isolates (BtMA-25 and BtMA-401) indicated the presence of molecular mass consistent with the proteins Cry4Aa, Cry11Aa, and Cyt1, similar to the profile of B. thuringiensis var. israelensis.
Further Research:
- While this study revealed the larvicidal potential of B. thuringiensis isolates from Cerrado soils, further research is needed to elucidate other genes associated with the production of insecticidal toxins in these isolates.
References
- Lobo, K. D. S., Soares-da-Silva, J., Silva, M. C. D., Tadei, W. P., Polanczyk, R. A., & Pinheiro, V. C. S. (2018). Isolation and molecular characterization of Bacillus thuringiensis found in soils of the Cerrado region of Brazil, and their toxicity to Aedes aegypti larvae. Revista Brasileira de Entomologia, 62(1), 5-12.
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