Bt Research 2025, Vol.16, No.2, 63-69 http://microbescipublisher.com/index.php/bt 63 Research Insight Open Access Role of Plasmids in the Horizontal Gene Transfer Among Bt Strains Jun Wang, Qikun Huang Tropical Microbial Resources Research Center, Cuixi Academy of Biotechnology, Zhuji, 311800, Zhejiang, China Corresponding author: qikun.huang@cuixi.org Bt Research, 2025, Vol.16, No.2 doi: 10.5376/bt.2025.16.0008 Received: 30 Jan., 2025 Accepted: 09 Mar., 2025 Published: 25 Mar., 2025 Copyright © 2025 Wang and Huang, 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: Wang J., and Huang Q.K., 2025, Role of plasmids in the horizontal gene transfer among Bt strains, Bt Research, 16(2): 63-69 (doi: 10.5376/bt.2025.16.0008) Abstract This study introduces the significant role of plasmids in horizontal gene transfer (HGT) in Bacillus thuringiensis (Bt) strains, summarizes the types and structural characteristics of plasmids, as well as their roles in genetic diversity, ecological adaptation, and strain evolution, points out the technical limitations in current plasmidomics research, and proposes future research directions. It also emphasized the need for a comprehensive assessment of the ecological risks of plasmid transmission and to explore their application potential in agricultural biotechnology. This study aims to provide theoretical support and practical reference for understanding the genetic evolution mechanism of Bt strains and their application in pest control. Keywords Plasmid diversity; Horizontal gene transfer; Bacillus thuringiensis; Ecological adaptation 1 Introduction Plasmids are important mobile genetic elements in bacteria and play a core role in the ecological adaptation and evolution of bacteria such as Bacillus thuringiensis (Bt). They can carry genes related to antibiotic resistance, virulence and metabolism, making it easier for host strains to survive in specific environments. Plasmids also influence the evolutionary process of genes through high copy numbers and some special genetic mechanisms, such as genetic dominance, heteroplasmids and segregation drift. These characteristics make plasmids the main driving force for bacterial genetic diversity and adaptability (Bedhomme et al., 2017; Rodríguez-Beltrán et al., 2021; Tokuda and Shintani, 2024). In Bt strains, horizontal gene transfer (HGT) is mainly accomplished by relying on mobile genetic elements such as plasmids (Yu and Zhou, 2024). HGT includes three ways: transformation, transduction and conjugation, among which conjugated plasmids are the most important. They can be transferred among different strains and even different species, allowing genes such as resistance and virulence to spread rapidly. The biofilm environment and the uptake of exogenous DNA also provide "hotspots" for plasmid-mediated HGT, accelerating the genetic diversity and adaptive evolution of the Bt microbiota (Harrison and Brockhurst, 2012; Evans et al., 2020; Vincent et al., 2024). This study summarizes the main mechanisms by which plasmids perform HGT among Bt strains, analyzes their roles in genetic diversity, ecological adaptation and resistance spread, and also explores the impact of plasmid-mediated HGT on the evolution and ecological functions of Bt strains. This study aims to provide a theoretical basis for understanding the dynamics of bacterial populations and the transmission of resistance genes. 2 Plasmid Diversity in Bt Strains 2.1 Types of plasmids: cry-carrying plasmids, conjugative plasmids, cryptic plasmids AmongBt (Bacillus thuringiensis) strains, there are various types of plasmids, mainly including plasmids carrying the cry gene, conjugated plasmids and cryptic plasmids. Plasmids carrying the cry gene are the genetic basis for Bt to produce insecticidal crystalline protein (Cry protein). This type of plasmid is widely distributed among different strains and is usually associated with specific insecticidal lineages (Apaydin et al., 2005; Wang et al., 2020). The conjugation plasmid has the ability of self-transfer and is an important medium for horizontal gene transfer between Bt strains. Although cryptoplasmids do not directly encode known functional genes, they may provide a potential platform for gene recombination and the evolution of new functions (Nair et al., 2018).
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