Bt Research 2025, Vol.16, No.2, 47-54 http://microbescipublisher.com/index.php/bt 47 Review Article Open Access Plasmid Diversity and Its Contribution to the Adaptation of Bt Strains Weichang Wu, Shiying Yu Biotechnology Research Center, Cuixi Academy of Biotechnology, Zhuji, 311800, China Corresponding author: shiying.yu@cuixi.org Bt Research, 2025, Vol.16, No.2 doi: 10.5376/bt.2025.16.0006 Received: 12 Jan., 2025 Accepted: 26 Feb., 2025 Published: 08 Mar., 2025 Copyright © 2025 Wu and Yu, 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: Wu W.C., and Yu S.Y., 2025, Plasmid diversity and its contribution to the adaptation of Bt strains, Bt Research, 16(2): 47-54 (doi: 10.5376/bt.2025.16.0006) Abstract Bacillus thuringiensis (Bt) is widely used in agriculture and public health because it can produce insecticidal proteins. It has many types of plasmids, and the differences in plasmids are precisely the important factors determining the strain's adaptability to the environment and its insecticidal range. This study introduces the main types of Bt plasmids, their replication and transfer patterns, as well as the latest research progress in plasmidomics. It explains some key functional genes carried on plasmids and analyzes the role of plasmid diversity in strain evolution, resistance transmission, niche differentiation and field application. It also pointed out the technical limitations and theoretical deficiencies existing in the current research and proposed future research directions. This study aims to provide references for the improvement of Bt strains and the development of new biological control strategies. Keywords Bacillus thuringiensis (Bt); Plasmid diversity; Horizontal gene transfer; Ecological adaptation; Biocontrol 1 Introduction Bacillus thuringiensis (Bt) is an insect pathogen that is widely used in agriculture and public health (Bravo et al., 2011; Sanahuja et al., 2011; Zhang, 2024). Bt can produce insecticidal proteins, such as δ -endotoxin, and thus has been developed into a biopesticide. It is regarded as an effective, safe and environmentally friendly method for pest control. Researchers around the world are constantly seeking new Bt strain resources in order to discover more types of insecticidal proteins that can also address the resistance problem caused by pests (Nair et al., 2018; Pacheco et al., 2021). In different ecological environments, there are still many Bt strains that have not been developed and utilized, and these strains may bring new insecticidal potential. The genetic diversity of Bt strains mainly stems from the plasmids they carry. Plasmids not only contain insecticidal genes such as cry and vip, but may also carry some virulence genes and genes related to adaptability. Through horizontal gene transfer, Bt can obtain new plasmids, thereby expanding its insecticidal range and enhancing its adaptability to the environment. Studies have found that the diversity of plasmids directly affects the types and quantities of insecticidal proteins in Bt and also determines its toxicity to different insects (Nair et al., 2018). In addition, plasmid recombination and gene insertion can also generate new protein combinations, which will increase the application potential of Bt in pest control (Wang et al., 2020; Pacheco et al., 2021). This study summarized the types and functional genes of plasmids in Bt strains, analyzed the influence of plasmid diversity on insecticidal lineages and ecological adaptability, and also explored the role of plasmid recombination and horizontal transfer in the evolution and application of Bt. This study aims to provide theoretical references and practical guidance for the application of Bt in biological control and the development of new insecticidal proteins. 2 Genetic Basis of Plasmid Diversity in Bt 2.1 Classification of plasmids: cry plasmids, Conjugative plasmids, and cryptic plasmids There are mainly three types of plasmids for Bt: cry plasmids, Conjugative plasmids and cryptic plasmids. The cry plasmid carries insecticidal protein genes, such as Cry and Vip proteins, which are the key for Bt strains to control pests. Studies have found that the distribution of cry genes varies greatly among different Bt strains. Some plasmids can also carry multiple genes simultaneously. For example, cry9A and vip3A in the same plasmid will jointly exert a stronger insecticidal effect (Wang et al., 2020). Conjugative plasmids can transfer themselves and
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