Bt Research 2025, Vol.16, No.4, 125-135 http://microbescipublisher.com/index.php/bt 130 5.2 Integration with genetically modified crops Integrating the Bt gene into the genome of crops has completely transformed the way pests are controlled in agriculture. Bt genetically modified crops, such as cotton and corn, are all designed to express insecticidal proteins that protect the crops from major pests throughout the growing season. These crops are widely cultivated all over the world. Since 1996, the planting area of Bt crops has increased by more than 100 times and exceeded 190 million hectares by 2019 (Li et al., 2022). The Bt gene in these crops can be stably passed on to the offspring and continuously expressed. This not only improves the agronomic traits of the crops, but also reduces the use of pesticides and increases the economic value. When using Bt genes to modify plants, the codons of the genes are usually optimized, and plant-specific promoters are also employed to enable the Bt genes to be better expressed and exert better effects. The Bt protein produced by genetically modified crops is different in structure and function from that produced by natural Bt bacteria. Therefore, a comprehensive biosafety assessment and environmental impact assessment must be conducted before commercial promotion. 5.3 Industrial practice of plasmid engineering and market performance of commercial strains The large-scale industrial production of Bt biopesticides cannot do without reliable plasmid engineering technology, which can ensure high output, stable and safe products. Innovations in strain and vector engineering - such as optimizing the plasmid's skeleton structure to make it more stable, have higher yields, and facilitate subsequent purification - have all enhanced the cost-effectiveness of Bt biopesticide production and made it easier to scale up production (Bower and Prather, 2009). In addition, the use of efficient transformation systems (such as electroporation technology) and the development of high-yield production strains have further enhanced the commercial feasibility of the modified Bt products (Nakamura, 2020). In the commercial market, BT-based biopesticides and genetically modified crops occupy a major position in global microbial pest control, accounting for approximately 90% of global biopesticide usage (Li et al., 2022). These products have been successfully promoted because they are only effective against specific pests, have high safety and a wide range of applications. The current focus of research is to continue improving plasmid design, enhancing environmental safety, and optimizing resistance management methods. This can not only keep the market growing continuously, but also ensure the long-term effectiveness of the product. 6 Current Challenges and Limitations 6.1 Biosafety issues of engineering plasmids and potential risks of gene transfer The application of engineered Bt plasmids in agriculture has raised significant biosafety issues, particularly regarding how long insecticidal genes can remain in the environment and whether gene transfer is possible. Bt proteins produced by modified strains and transgenic plants are regarded as foreign substances in the environment, and their structures and functions are different from those of natural Bt toxins. These proteins can remain in the soil for a period of time, combine with organic matter, and maintain insecticidal activity for a relatively long time. This may affect the variety and quantity of microorganisms in the soil as well as the normal operation of the entire ecosystem. Therefore, before releasing BT-modified organisms into the wild or conducting commercial production, a comprehensive biosafety assessment must be carried out to determine their changes in the environment and their ecological impact (Li et al., 2022). The main risk associated with engineered plasmids is the possibility that their genes may be transferred to non-target microorganisms. Plasmids (especially those with binding elements) may allow insecticidal genes or resistance genes to spread into host organisms they were not originally intended to act on, which has raised concerns - fears of unexpected ecological consequences and even the emergence of new, potentially harmful microbial strains. Current regulatory rules are becoming increasingly strict, requiring the removal of antibiotic resistance markers and binding systems from large engineering plasmids to reduce these risks. Meanwhile, researchers are also developing new plasmid designs centered on biosafety to limit gene transfer and ensure that genes do not spread at will.
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