Bt Research 2024, Vol.15, No.3, 141-153 http://microbescipublisher.com/index.php/bt 142 2 Overview of Bt Strains 2.1 Diversity of Bt strains Bacillus thuringiensis (Bt) strains display a remarkable degree of genetic diversity, which significantly contributes to their efficacy as biopesticides. This diversity arises from the extensive variety of Cry and Cyt toxins produced by different Bt strains, which target specific insect orders. Studies employing techniques such as random amplified polymorphic DNA (RAPD) analysis have shown significant genetic variation among Bt strains. For instance, research on Bt isolates from Kuwait revealed the existence of multiple genetically distinct groups within the Bt population, underscoring the complexity and adaptability of this species (Qasem et al., 2015). The genome sequencing of Bt strains such as Bt-UNVM_94 from Argentina has highlighted their ability to produce a broad spectrum of insecticidal proteins, demonstrating dual activity against lepidopteran and coleopteran pests (Peralta et al., 2021). This genetic diversity not only enhances the effectiveness of Bt as a biopesticide but also aids in overcoming insect resistance, a growing challenge in pest management. The broad genetic variation found in Bt strains ensures a continuous supply of novel toxins that can be leveraged to develop new biopesticides, thereby maintaining the long-term efficacy of Bt-based pest control strategies. 2.2 Key characteristics and applications Bacillus thuringiensis is characterized by its ability to produce crystalline inclusions during sporulation. These inclusions contain delta-endotoxins, specifically Cry and Cyt proteins, which are toxic to a wide range of insect larvae upon ingestion. The insecticidal properties of Bt make it an invaluable tool in integrated pest management (IPM). For example, the Brazilian strain Bt 147 has been noted for its high insecticidal activity against various insect larvae, providing an environmentally friendly alternative to traditional chemical pesticides (Barbosa et al., 2015). Bt's specificity to target pests minimizes collateral damage to non-target organisms, making it a safer option for pest control. Another notable strain is Bt-UNVM-84, which shows significant insecticidal activity against the cotton boll weevil, a major pest in the cotton industry, thereby contributing to sustainable agricultural practices (Sauka et al., 2023). The wide array of toxins produced by different Bt strains allows for targeted pest control, reducing the likelihood of pest resistance development. Bt has been employed in genetically modified crops, such as Bt corn and Bt cotton, which express Bt toxins and provide built-in pest resistance, further reducing the need for chemical pesticides. The versatility and effectiveness of Bt underscore its pivotal role in modern agriculture. 2.3 Historical perspective on Bt research The history of Bacillus thuringiensis research dates back to its discovery in 1901 by Japanese bacteriologist Ishiwata Shigetane. Initially identified as a pathogen in silkworms, Bt's potential as a biological control agent was recognized in the mid-20th century. The first commercial Bt-based biopesticide was developed in the 1950s, marking the beginning of extensive research into its insecticidal properties and applications. Over the decades, advancements in molecular biology and genomics have significantly enhanced our understanding of Bt. The sequencing of various Bt strains, such as BM-BT15426 and Bt-UNVM_94, has revealed insights into their genetic makeup and pathogenic mechanisms (Liu et al., 2017; Peralta et al., 2021). These genomic studies have facilitated the identification of numerous Cry and Cyt toxins, broadening the scope of Bt's applications. Research has explored Bt's role in integrated pest management, highlighting its environmental benefits compared to chemical pesticides. Historical research has also focused on the mechanisms of insect resistance to Bt, leading to the development of strategies to mitigate this challenge. Overall, the historical evolution of Bt research reflects its growing importance in sustainable agriculture and its potential to address future pest management challenges. 3 Methods for Phylogenetic Analysis 3.1 Sample collection and identification Sample collection is a crucial first step in the phylogenetic analysis of Bacillus thuringiensis (Bt) strains. The process typically involves isolating Bt from various environmental sources such as soil, plants, and insect larvae.
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