Bt Research 2025, Vol.16, No.2, 70-78 http://microbescipublisher.com/index.php/bt 74 pressures and remain competitive in natural and agricultural ecosystems (Berçot et al., 2023; Cao et al., 2023). In addition, Bt strains often carry some genes that can promote plant growth or have antifungal effects, enriching their ecological functions (Yilmaz et al., 2024; Cao et al., 2025). 6 Case Study: Comparative Analysis of Bt Populations in Contrasting Ecosystems 6.1 Study sites, sampling strategy, and molecular methods This case study mainly compares the genetic structure of the Bt population in different ecosystems. Researchers selected biological environments (such as the rhizosphere of plants and insect-related environments) and abiotic environments (such as inorganic surfaces and soil), and collected Bt samples respectively. Longitudinal whole-population genome sequencing was used in the experiment. High-depth sequencing was conducted on the Bt population at different time points and in different environments to detect variations such as SNPS, Indels, and large fragment insertions. The genetic diversity and evolutionary dynamics were comprehensively analyzed (Hu et al., 2023). In addition, some studies have conducted multi-site enzyme electrophoresis, MLST and toxin genotype analysis on Bt strains in different geographical regions and ecosystems (such as forest soil, farmland, and endogenous environment of wild plants) (Sun et al., 2021; Espinoza-Vergara et al., 2023). 6.2 Key findings on genetic structure and diversity indices It was found that Bt has a higher mutation frequency, more diverse genotypes and a faster evolution speed in biological environments (such as the rhizosphere and within insects). However, in abiotic environments (such as inorganic surfaces), diversity is relatively low and clonal expansion is more obvious (Hu et al., 2023). Insertion sequences (IS elements) play an important role in Bt adaptation to different environments, promoting rapid changes in genomic structure (Sun et al., 2021). Bt populations in different ecosystems vary greatly in toxin genes, plasmid profiles and functional genes. Some strains accumulated multiple toxin genes targeting different insects in specific ecological niches (such as aquatic or insect-related environments), indicating that their ecological adaptability and functional diversity have both improved (Zheng et al., 2017). The genetic differentiation index (Fst) and diversity index (Shannon index) also show significant differences in different ecosystems. The genetic diversity and evolutionary rate of Bt populations in biological environments are higher. 6.3 Ecological and practical implications for biocontrol applications The genetic diversity and population structure of Bt in different ecosystems will directly affect its application potential in biological control. Those Bt strains with diverse genotypes and multiple toxin genes can help expand the insecticidal spectrum, delay the evolution of pest resistance, and also improve the adaptability of biocontrol agents in different environments (Zheng et al., 2017; Sun et al., 2021). Ecosystem types and environmental pressures can determine the evolutionary strategies and functional differentiation of Bt populations, which reminds us to consider their ecological origins and genetic backgrounds when screening and applying biocontrol strains (Hu et al., 2023). Meanwhile, the interaction between Bt and other microorganisms and plants in the environment will also affect its stability and safety in natural and agricultural ecosystems. Therefore, multi-level ecological assessment should be conducted before biocontrol application (Figure 2) (Belousova et al., 2021; Espinoza-Vergara et al., 2023). 7 Challenges and Research Gaps 7.1 Limitations in sampling and molecular resolution At present, there are two main problems in the research on the genetic diversity of Bt. One is that there are too few sampling points. Many studies have only been conducted in a few regions or ecosystems, and the results may not represent the true diversity and ecological adaptability of Bt globally (Da Costa Fernandes et al., 2021; Berçot et al., 2023). Another issue is that the resolution of the molecular method is insufficient. Traditional methods such as 16S rRNA, RAPD, and rep-PCR can reveal some diversity, but it is difficult to distinguish closely related strains, and they are not very suitable for studying plasmids and mobile genetic elements (Mishra et al., 2017; Rabha et al., 2023). Although high-throughput sequencing has begun to be used in some studies, its systematic application worldwide is still insufficient, and it is not very sensitive to genotypes with complex population structures or very small numbers (Gillis et al., 2018; Biggel et al., 2022).
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