Bt Research 2025, Vol.16, No.5, 182-193 http://microbescipublisher.com/index.php/bt 189 Bt prototoxin requires these proteases to remove nontoxic fragments at the N- and C-terminal ends to be converted into activated toxins (Guo et al., 2020). Therefore, an appropriate amount of enzyme activity is necessary. Other chemical components in the gut environment may also affect Bt metabolism and virulence. For example, certain secondary compounds in plants fed by plant-eating insects may inhibit Bt metabolic enzymes, thereby reducing the effect of Bt infection. 6.3 Feedback from insect immune response on Bt metabolism When Bt successfully breaks through the insect midgut barrier and enters the blood body cavity, the host's humoral and cellular immunity will be quickly activated to fight the invading pathogen. The immune response of insects includes the production of antimicrobial peptides, activation of phenol oxidase cascades to cause blood aggregation, phagocytosis of bacteria, etc. These immune effects also have feedback effects on the metabolic state of Bt (Sun et al., 2025). Antimicrobial peptides produced by insects can act directly on the Bt cell membrane, causing pores and metabolic disorders. Faced with this attack, Bt may induce membrane repair mechanisms and stress metabolic pathways, such as enhancing lipid metabolism to increase membrane steroids against antimicrobial peptide inserts. Some studies have pointed out that when Bt infects rhododendron moth, it triggers a strong immune response in the intestine, including activation of a series of antibacterial genes, but these immune genes are downregulated after Bt destroys the intestinal flora. This suggests that Bt weakens host immunity by destroying insect intestinal microbial balance, thereby reducing its killing to itself. Oxidative stress in insect immune responses can put stress on Bt (Wu et al., 2022). Insect blood cells can kill bacteria by producing reactive oxygen species such as hydrogen peroxide (ROS) through DUOX enzyme. 7 Case Analysis: Metabolic Mechanism of Bt in Corn Bordy Control 7.1 Bt is the key metabolic link in the pathogenesis of corn borer Corn borer (Osrinia furnacalis) is an important feeding pest on corn, and Bt and its toxins play a central role in the biological control of corn borer. During the Bt-corn borer interaction, the development of Bt pathogenicity involves a series of key metabolic links. First, the survival of Bt in the midgut of corn borer and the release of toxins. The midgut of corn borer larvae is highly alkaline and rich in proteases, which provides conditions for the dissolution and activation of Bt crystal toxins. Studies have shown that Bt in the intestine of corn borer will enhance glycolysis and organic acid output to neutralize the local environment to help itself survive (Peng et al., 2024). This metabolic adjustment ensures that Bt successfully enters the spore production and toxin expression stages in the host. The proliferation and colonization of Bt in the intestines of corn borer is a pathogenic amplification step. Bt proliferation requires nutrients from the host. Corn borer feeds on plant tissues, and its intestinal contents are relatively large and free amino acids are limited. The immune response of corn borer larvae can affect the Bt infection process. Recent studies have found that the intestinal flora of corn borer undergoes drastic changes under the action of Bt toxin, and many symbiotic bacteria die or escape from the intestine, resulting in downregulation of host immune gene expression (Li et al., 2020; Xu et al., 2023). During the spread of Bt in corn borer and host death stage, Bt reproduces in large quantities and uses host carcasses to form new spores in preparation for the next round of transmission (Figure 3). In field prevention and control, the pathogenic efficiency of Bt on corn borer is affected by many factors, such as the dosage form of the application, the target insect age, the ambient temperature and humidity, etc. 7.2 Metabolic support mechanism of Cry1Ab toxin Cry1Ab is one of the main insecticidal crystal proteins used by Bt to prevent and control corn borer, and is widely used in both natural Bt strains and trans-Bt gene corn. The successful play of Cry1Ab toxin is closely related to metabolic optimization in Bt strains and host plants. In terms of Bt strains, producing high levels of Cry1Ab requires a strong metabolic supply. Many industrialized Bt preparation strains have obtained higher Cry1Ab expression through mutation and domestication, which often involve changes in metabolic pathways. In transgenic Bt corn, the expression of Cry1Ab toxin also depends on metabolic optimization. As a "factory" for the production of Cry1Ab, plants must contain the synthesis of large amounts of exogenous proteins without
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