Bt Research 2025, Vol.16, No.3, 110-117 http://microbescipublisher.com/index.php/bt 111 2 Environmental Stressors Affecting Bacillus thuringiensis 2.1 Abiotic stresses Abiotic stresses include salt stress, ultraviolet rays, oxidative stress and heavy metal pollution. Salt stress is very common in agricultural environments and can disrupt the osmotic balance of Bt, reducing its survival rate. Research has found that some salt-tolerant Bt strains (such as PM25) can enhance their adaptability to salt stress by up-regulating the expression of antioxidant enzymes (SOD and APX) and related genes. These strains can also help plants grow better and improve stress resistance (Ali et al., 2022). Ultraviolet rays and oxidative stress can also reduce the survival rate and tolerance of Bt. Some genes (such as biotin synthesis gene bioC, urea cycle related gene rocF/argG) play important roles in resisting such stress (Zhang et al., 2024). In addition, Bt can also degrade some environmental pollutants, such as heavy metals, organic pollutants and pesticides, which indicates that it has a strong environmental adaptability (Jouzani et al., 2017; Wu et al., 2023). 2.2 Biotic stresses Biological stress mainly stems from the competition and antagonism among microorganisms, as well as the immune response of insect hosts. Bt can form complex relationships with many local bacteria and fungi in the soil. Some bacteria (such as Pseudomonas fluorescetes) can secrete toxic substances that inhibit the growth of Bt and induce it to form spores, thereby affecting reproduction. In biological control, Bt also needs to confront the evolution of pest resistance and the ecological impact on non-target organisms (Argolo-Filho and Loguercio, 2013; Pinos et al., 2021). However, Bt itself can produce antimicrobial peptides (such as thuricins), which can enhance its ability to compete with other microorganisms (Belousova et al., 2021) (Figure 1). Figure 1 The effect of Bt on organisms within the natural ecosystems. Black arrows indicate possible detrimental effects; green arrows denote possible beneficial effects. Solid arrows denote direct effects; dotted arrows stand for indirect effects. Black wavy arrows indicate Bt transfer through plant tissues (Adopted from Belousova et al., 2021) 2.3 Industrial/fermentation stresses In industrial production and fermentation, Bt often encounters pressures such as high temperatures, oxidation, pH fluctuations and nutrient deficiencies. Studies have shown that Bt spores have a strong tolerance to damp heat and ultraviolet rays. In commercialized preparations, the formulation can further protect spores and make them more resilient (Zhao et al., 2023). Meanwhile, environmental changes during the fermentation process can affect the growth of Bt, the expression of insecticidal proteins and the stability of the product. Therefore, in production, it is necessary to ensure better results by regulating fermentation conditions and selecting strains with strong stress tolerance (Jouzani et al., 2017).
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