Bt Research 2024, Vol.15, No.2, 76-86 http://microbescipublisher.com/index.php/bt 76 Research Report Open Access Characterization of Plasmid-encoded Toxins inBacillus thuringiensis Ziyi Dong, Zhongqi Wu Institute of Life Sciences, Jiyang College, Zhejiang A&F University, Zhuji, 311800, Zhejiang, China Corresponding author: zhongqi.wu@jicat.org Bt Research, 2024, Vol.15, No.2 doi: 10.5376/bt.2024.15.0008 Received: 05 Feb., 2024 Accepted: 18 Mar., 2024 Published: 06 Apr., 2024 Copyright © 2024 Dong and Wu, This is an open access article published under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Preferred citation for this article: Dong Z.Y., and Wu Z.Q., 2024, Characterization of Plasmid-encoded Toxins in Bacillus thuringiensis, Bt Research, 15(2): 76-86 (doi: 10.5376/bt.2024.15.0008) Abstract Bacillus thuringiensis (Bt) is a bacterium widely used in pest management due to its production of plasmid-encoded toxins. These toxins play a crucial role in Bt’s insecticidal properties. This study aims to provide a comprehensive overview of plasmid-encoded toxins in Bt, their genetic and molecular mechanisms, functional analyses, methods of characterization, ecological implications, and applications in pest management. The study begins by exploring the types and characteristics of plasmids in Bt, highlighting their role in Bt genetics and their diversity among different Bt strains. It then delves into the various plasmid-encoded toxins, including Cry, Cyt, Vip, and other toxins, explaining their gene structure, regulation, and mechanisms of horizontal gene transfer. The functional analysis section examines the insecticidal activity, specificity, and mechanisms of toxicity of these toxins. Methods for characterizing these toxins, such as genomic sequencing, proteomic analysis, functional assays, and bioinformatics approaches, are also discussed. The ecological and evolutionary implications of plasmid-encoded toxins, including their role in Bt evolution, impact on host range and virulence, and environmental persistence, are considered. Finally, the study discusses the applications of Bt toxins in pest management, focusing on Bt-based biopesticides, transgenic crops expressing Bt toxins, and strategies to combat resistance. This study underscores the importance of plasmid-encoded toxins in Bt, summarizing key findings and highlighting their significance in pest management. Future research should focus on advancing our understanding of these toxins to enhance their efficacy and sustainability in agricultural practices. Keywords Bacillus thuringiensis; Plasmid-encoded toxins; Cry toxins; Pest management; Horizontal gene transfer 1 Introduction Bacillus thuringiensis (Bt) is a Gram-positive, soil-dwelling bacterium that has been extensively studied for its insecticidal properties. Bt produces crystal (Cry) and cytolytic (Cyt) proteins during sporulation, which are toxic to a wide range of insect pests. These proteins have been utilized in biopesticides and genetically modified crops to control agricultural pests, reducing the reliance on chemical insecticides and promoting environmentally friendly pest management strategies (Pérez et al., 2005; Pardo-López et al., 2013; Liang et al., 2022). The insecticidal properties of Bt are largely attributed to the Cry and Cyt proteins, many of which are encoded by plasmids. These plasmid-encoded toxins are crucial for the bacterium's pathogenicity and effectiveness as a biocontrol agent. For instance, the Cry11Aa and Cyt1Aa proteins produced by Bacillus thuringiensis subsp. israelensis are known to synergize, enhancing their toxicity against mosquito larvae and overcoming insect resistance (Pérez et al., 2005). Additionally, novel Cry proteins such as Cry31Aa and Cry78Ba1 have been identified, showing high nematicidal and insecticidal activities, respectively, and offering potential for the control of specific pests like rice planthopper and plant parasitic nematodes (Cao et al., 2020; Liang et al., 2022). Understanding the molecular mechanisms and interactions of these toxins is essential for developing new strategies to combat insect resistance and improve the efficacy of Bt-based biopesticides (Pardo-López et al., 2013; Guo et al., 2019). The study is to provide a comprehensive overview of the current knowledge on plasmid-encoded toxins in Bacillus thuringiensis. This includes elucidating the molecular mechanisms of action and synergism of key Cry and Cyt proteins. Additionally, the study explore the genetic and structural basis of insect resistance to these toxins. Another goal is to highlight recent advancements in the identification and characterization of novel Cry
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