Bt Research 2024, Vol.15, No.1, 20-29 http://microbescipublisher.com/index.php/bt 24 quercetin 2,3-dioxygenase, in Bt strains underscores the role of natural selection in promoting traits that enhance the survival and competitiveness of these bacteria in diverse environments (Adeniji et al., 2021). 6 Case Studies of Specific Bt Strains 6.1 Comparison of highly virulent strains Highly virulent strains of Bacillus thuringiensis (Bt) have been extensively studied to understand their genetic and proteomic profiles, which contribute to their insecticidal properties. For instance, the Bt strain GR007, which is toxic to Spodoptera frugiperda and Manduca sexta larvae, has been sequenced to reveal multiple pesticidal protein genes, including 10 Cry genes and two Vip genes. Proteomic analysis of the parasporal crystals of GR007 identified eight Cry proteins, with Cry1Bb and Cry1Ka showing the highest activity against S. frugiperda and M. sexta larvae, respectively (Pacheco et al., 2021). Another highly virulent strain, Bt X022, isolated from soil in China, showed strong insecticidal activity against several Lepidopteran pests. Comparative genomic and proteomic analyses revealed the presence of genes coding for Cry1Ac, Cry1Ia, Cry2Ab, and Vip3A proteins, with three insecticidal crystal proteins detected during the spore-release period (Quan et al., 2016). 6.2 Analysis of Bt strains with novel traits Novel traits in Bt strains can provide insights into their unique insecticidal properties and potential applications. The Bt strain BLB406, for example, exhibits larvicidal activity against Aedes aegypti larvae and contains a unique combination of toxins, including five Cry genes (Cry11, Cry22, Cry2, Cry60, Cry64) and two Vip4 genes. This combination offers potential larvicidal and anti-cancer activities, making BLB406 a promising candidate for biotechnological applications (Zghal et al., 2018). Additionally, the Bt strain BM-Bt15426 has been sequenced to identify its genetic characteristics, revealing 21 virulence factors and nine antibiotic resistance genes. This strain's genome provides valuable information for further studies on its pathogenic mechanisms and phenotypes (Liu et al., 2017). 6.3 Evolutionary insights from comparative genomics Comparative genomic analyses of Bt strains have provided significant evolutionary insights. The distribution of genomic virulence determinants in various Bt strains does not align with the established serotyping classification, indicating that serotyping may not accurately reflect the phylogenetic relationships within the species. Comparative genomic and proteomic techniques have shown that core gene sequences and accessory protein genes do not serve as distinctive bases for serovar attribution, emphasizing the need for phylogenomics approaches for accurate strain classification (Figure 2) (Shikov et al., 2021). Shikov et al. (2021) presented a study that showcased the spore morphology, growth curves, protein electrophoresis profiles, and the distribution of functional genome classifications (COG) among different Bacillus thuringiensis (Bt) strains. Although there are similarities in morphology and growth characteristics among different Bt strains, they exhibit significant differences in protein expression and functional genome classification. Comparative genomic and proteomic techniques have not only revealed the evolutionary relationships among Bt strains but also provided profound insights into their virulence mechanisms. These findings underscore the importance of adopting systematic genomic approaches for accurate strain classification, thus better understanding the evolution and ecological adaptability of Bt strains. The study of Bt strain 4.0718 revealed that not all products deduced from the annotated genome could be identified in the proteomic data, suggesting that some genes may be silenced or expressed at very low levels. This analysis highlighted the importance of regulatory networks in spore formation and the potential for constructing highly virulent engineered bacteria (Rang et al., 2015).
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