Bt Research 2025, Vol.16, No.5, 214-223 http://microbescipublisher.com/index.php/bt 218 compared the dynamics of exogenous proteins in soil between Bt rice and non-Bt rice. The results show that during the rice growing season, the concentration of Cry1Ab/1Ac protein at the rhizosphere soil of Bt rice can be detected; however, after harvest, the content of Bt protein in the soil rapidly decreases with straw and root degradation, and almost drops below the detection limit 60 days after harvest (Li et al., 2007; Wang et al., 2022). This shows that the Bt toxin in plant residues will basically degrade within about 2 months. The decomposition process of plant residues is a process in which Bt protein release and degradation is parallel. Figure 1 Action Mechanism of Bacillus thuringiensis Cry Proteins in Insect Larval Midgut (Adopted from Bangaru, 2025) Image caption: A: Formation of protoxin crystals during bacterial sporulation, B: Dissolution and activation of protoxins by insectmidgut proteases in an alkaline pH environment, C: Interaction of activated toxins with specific midgut epithelialreceptors (e.g. cadherins, aminopeptidases), D: Disruption of epithelial cells via pore formation, leading to cellulardamage and leakage, ultimately causing insect death21 (Adopted from Bangaru, 2025) 5.2 The regulation of organic matter content on degradation rate The levels of organic matter in environmental media often affect the degradation of Bt toxins through a variety of pathways. Organic matter can affect the adsorption state and stability of Bt protein. Soils or sediments with high organic matter content provide more organic colloids and humus, and Bt toxins can easily bind to form macromolecular complexes, thereby temporarily reducing the accessibility of microorganisms to Bt proteins. This may be reflected in the initial stage of degradation as a decrease in the degradation rate of Bt toxin. However, organic matter is also a matrix for microbial growth, and a high organic matter environment often means a richer and more active microbial community (Ge et al., 2023). Therefore, from the middle and late stages, high organic matter content can often enhance the biodegradation potential of Bt toxins. When there is sufficient carbon source and nutrients in the environment, microorganisms reproduce vigorously and various decomposition enzymes (including proteases) are more active, thereby accelerating the mineralization of Bt protein. Returning organic matter such as straw to the field will significantly increase the level of soil organic matter and change soil microbial activity. Studies have shown that in rice fields where straw is returned to the field for many years, the soil carbon and nitrogen content has increased significantly, and the microbial mass carbon and enzyme activity have also increased accordingly. Under such ground conditions, the Bt toxins remaining in Bt crops are more likely to be rapidly degraded and less likely to accumulate (Zhou et al., 2018; Ge et al., 2023). 5.3 Dynamic changes of Bt toxins under farm farming management Farmland farming and residue management measures significantly affect the dynamic changes of Bt toxins in the environment. In traditional agricultural practice, the harvested crop straw may choose to return directly to the field, incinerate or take it out of the field in different ways. Among them, direct return to the field, especially crushing
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