Bt Research 2024, Vol.15, No.2, 76-86 http://microbescipublisher.com/index.php/bt 77 proteins with potential applications in pest management. The study also discusses the implications of these findings for the development of more effective and sustainable biopesticides. By synthesizing information from multiple studies, this study aims to enhance our understanding of Bt toxins and their role in pest control, ultimately contributing to the advancement of agricultural biotechnology and integrated pest management practices. 2 Overview of Plasmids in Bt 2.1 Types and characteristics of plasmids Bacillus thuringiensis (Bt) harbors a variety of plasmids that play crucial roles in its insecticidal properties. These plasmids vary significantly in size and genetic content. For instance, the plasmid pTAND672-2 from Bt serovar israelensis is a 144 kb integrative and conjugative element (ICE) that carries mosquitocidal toxin genes, conjugation genes, and recombinase-encoding genes (Geng et al., 2023). Another example is the mega plasmid poh1 in Bt ATCC 10 792, which is 584,623 bps in size and contains genes responsible for antimicrobial, insecticidal, and antibiotic resistance activities (Chelliah et al., 2019). Additionally, the plasmid pH3-180 in the H3 strain of Bt carries a wide repertoire of mobile genetic elements and novel Cry proteins (Fayad et al., 2020). 2.2 Role of plasmids in Bt genetics Plasmids in Bt are pivotal for its genetic diversity and adaptability. They often carry genes encoding insecticidal toxins, such as Cry and Cyt proteins, which are essential for Bt's biopesticide properties. For example, the plasmid pIS56-63 in Bt subsp. thuringiensis strain IS5056 harbors the cry1Ab21 gene, which encodes a delta-endotoxin highly toxic to Trichoplusia ni larvae (Tanapongpipat et al., 2003; Murawska et al., 2014). Plasmids also facilitate horizontal gene transfer, enhancing the genetic variability and adaptability of Bt. The pTAND672-2 plasmid, for instance, can transfer between different bacterial species, contributing to the spread of mosquitocidal toxin genes (Figure 1) (Geng et al., 2023). Figure 1 Circular map comparison among pTAND672-2, pCH_133-e, and pBtoxis (Adopted from Geng et al., 2023) Image caption: pCH_133-e and pBtoxis display 77% and 43% coverage to pTAND672-2, respectively, with 100% identity. No plasmid replication/partition genes were predicted in the pBtoxis-like region in pTAND672-2. The overlap regions among the three plasmids contain several IS elements (Adopted from Geng et al., 2023)
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