Bt Research 2025, Vol.16, No.2, 63-69 http://microbescipublisher.com/index.php/bt 66 4.2 Transfer of antibiotic resistance and stress tolerance traits HGT can also cause the rapid spread of antibiotic resistance genes and stress tolerance genes. These genes can be transmitted among different Bt strains and different species, allowing the resistance phenotype to emerge and accumulate rapidly. This process exacerbates the problem of antibiotic resistance and makes Bt strains more likely to survive in complex environments (Lerminiaux and Cameron, 2019; Brito, 2021; Wang et al., 2025). Plasmids can also carry genes that respond to environmental stresses such as heavy metals and oxidative stress, enhancing the adaptability of strains (Harrison and Brockhurst, 2012; Brito, 2021). 4.3 Synergistic adaptations enhancing ecological fitness and competitiveness Plasmid-mediated HGT promotes the coadaptive evolution of Bt strains by integrating multiple beneficial genes. Plasmids with multiple functional genes enhance the ecological adaptability of strains and strengthen their competitive advantages in the microbial community (Brito, 2021). This coevolution is helpful for maintaining the co-adaptation relationship between plasmids and hosts, and also promotes the diversity of microbiota and the stability of ecosystems. 5 Ecological and Evolutionary Implications 5.1 Role of plasmid-mediated HGT in niche adaptation Plasmids can carry adaptive genes, such as resistance, metabolic or virulence genes, helping Bt strains quickly adapt to new ecological environments. Horizontal gene transfer (HGT) enables bacteria to acquire the ability to cope with environmental stresses such as toxins, antibiotics or heavy metals in a very short time, thereby expanding their ecological distribution range. Studies have shown that plasmids, as mobile genetic elements, can not only bring new traits but also enable bacterial populations to achieve "adaptive radiation" in different environments, accelerating ecological diversification (Wiedenbeck and Cohan, 2011; Hall et al., 2017; Petersen et al., 2019). 5.2 Contribution to strain diversity and persistence in natural environments Through frequent transfer of plasmids, beneficial genes can be rapidly exchanged between strains, forming groups with different functions. This diversity enables the strains to survive and compete for a long time in complex and variable natural environments (Hall et al., 2017). Plasmid-mediated gene transfer can also generate new ecological types in the population, promoting the emergence and persistence of new strains (Wiedenbeck and Cohan, 2011; Yang et al., 2024). 5.3 Influence on co-evolution with insect hosts and other microbes Plasmid-mediated HGT not only affects Bt strains themselves, but also profoundly alters their coevolution with insect hosts and other microorganisms. HGT can enable Bt strains to acquire new virulence factors or resistance mechanisms, alter their interactions with host insects, and promote coevolution similar to an "arms race" (Gluck-Thaler and Slot, 2015). Furthermore, plasmids act like "gene transporters" in the microbial community, promoting gene exchange among different species and reshaping the structure and functional network of the microbial community (Hall et al., 2017). 6 Case Study: Evidence of Plasmid-Mediated HGT in Bt 6.1 Representative study of plasmid transfer events among Bt strains The latest research has found that there is a highly efficient plasmid transfer between Bt and its closely related members of the genus Bacillus. Wang et al. (2025) achieved efficient plasmid transfer among wild-type Bt strains using the "cell-to-cell natural transformation" method (CTCNT-P), demonstrating that plasmid-mediated HGT is not only feasible but also highly efficient in the natural environment. This discovery provides direct evidence for the rapid spread of insecticidal genes and resistance genes among Bt strains. 6.2 Experimental approaches for tracing plasmid exchange In experiments, plasmid transfer events are usually tracked through marker genes and molecular detection methods. The CTCNT-P method uses antibiotic pressure to screen translators, combined with whole-genome
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