Molecular Pathogens 2024, Vol.15, No.5, 255-262 http://microbescipublisher.com/index.php/mp 258 results in spores with reduced stress resistance, highlighting the critical role of sRNAs in fine-tuning the sporulation process under stress conditions (Haq et al., 2021). The acetylation state of the histone-like protein HBsu affects both the process of sporulation and the resistance properties of spores, indicating a sophisticated regulatory mechanism involving post-translational modifications (Freire et al., 2023). 4.3 Adaptive benefits of sporulation under extreme stress conditions Sporulation provides significant adaptive benefits to B. subtilis under extreme stress conditions. The formation of highly resistant, dormant spores allows the bacterium to persist in harsh environments for extended periods. The protective mechanisms include the condensation of chromosomal DNA by small acid-soluble proteins (SASPs) and the histone-like protein HBsu, which are crucial for DNA protection against environmental insults. The evolutionary adaptation of sporulation genes, driven by gene gain events and horizontal gene transfer, has enhanced the ability of B. subtilis to survive in diverse and challenging ecosystems (Ramos-Silva et al., 2019). The stochastic nature of sporulation entry, driven by noise in the phosphorelay system, ensures that a subset of the population can rapidly respond to nutrient limitation, thereby increasing the overall survival chances of the community (Russell et al., 2017). 5 Genetic and Biotechnological Applications 5.1 Genetic basis of stress resistance The genetic basis of stress resistance in Bacillus subtilis is intricately linked to the regulation of alternative sigma factors, particularly SigB. SigB controls a vast array of genes, over 150, that are crucial for the bacterium's response to various stress conditions, including energy, environmental, and low-temperature stresses. This regulation allows B. subtilis to adapt and survive under adverse conditions by modulating gene expression to enhance stress resistance and manage sporulation processes. The acetylation of the histone-like protein HBsu plays a significant role in the packaging and protection of the spore chromosome, which is essential for the resistance properties of spores against environmental insults (Luu et al., 2022). 5.2 Genetic engineering of Bacillus subtilis for enhanced stress resistance Genetic engineering efforts have focused on manipulating specific genes to enhance the stress resistance of Bacillus subtilis. For instance, the deletion of single genes such as spo0A, spoIIIE, and spoIVBhas been shown to completely block spore formation, which can be advantageous for industrial applications where high cell density and product yield are desired. These non-sporulating mutants exhibit distinct physiological traits and enhanced capabilities for producing enzymes and secondary metabolites, such as surfactin (Wang et al., 2020). Mutations in the rsbUgene, which encodes a phosphatase that activates SigB, have been found to increase resistance to ethanol stress, although they may also inhibit sporulation (Rothstein et al., 2017). 5.3 Biotechnological applications of Bacillus subtilis in industry Bacillus subtilis has significant biotechnological applications, particularly in agriculture and environmental management. As a plant-growth-promoting rhizobacterium (PGPR), B. subtilis enhances plant growth and stress tolerance through mechanisms such as the induction of systemic resistance, antibiosis, and competitive exclusion. It produces secondary metabolites, hormones, and enzymes that help plants defend against pathogens and improve nutrient uptake (Hashem et al., 2019). B. subtilis has been used to reduce antibiotic resistance genes in animal sludge during vermicomposting, thereby improving the quality of the compost and promoting the growth of beneficial microbial communities (Hao et al., 2022). The production of high-molecular-weight γ-polyglutamic acid (γ-PGA) by B. subtilis also highlights its potential in enhancing soil fertility and plant security in agricultural ecosystems (Bai et al., 2022). 6 Case Studies onBacillus subtilis Stress Resistance and Sporulation 6.1 Stress resistance in industrial strains: a comparative analysis Bacillus subtilis is renowned for its ability to withstand various environmental stresses, a trait that is particularly valuable in industrial applications. The stress-responsive alternative sigma factor SigB plays a crucial role in this resistance. SigB controls a wide array of genes involved in stress response, adaptation, and survival, including
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