Molecular Pathogens 2024, Vol.15, No.5, 255-262 http://microbescipublisher.com/index.php/mp 256 2 Stress Resistance Mechanisms inBacillus subtilis 2.1 General stress response pathways Bacillus subtilis employs a variety of stress response mechanisms to adapt to environmental changes. The alternative sigma factor SigB plays a crucial role in the general stress response, regulating over 150 genes involved in adaptation and survival under stress conditions. SigB activation is mediated through three distinct pathways that respond to energy, environmental, and low-temperature stresses. This factor also influences spore and biofilm formation, linking stress response to these critical survival strategies (Fimlaid and Shen, 2015; Tran et al., 2018). 2.2 Oxidative stress resistance Oxidative stress resistance in B. subtilis is primarily managed by the transcription factor Spx, which activates the thiol stress response regulon. Spx upregulates genes essential for managing oxidative stress and can inhibit the transcription of translation-related genes to conserve resources under stress conditions. Additionally, the stressosome complex and RsbP are vital for SigB activation, providing cross-protection against oxidative and nitrosative stress (Schäfer et al., 2018). 2.3 Osmotic stress response In response to osmotic stress, B. subtilis activates the proline biosynthetic pathway, which is regulated by the osmotically controlled proHJ promoter. This pathway allows the accumulation of proline, a compatible solute that helps the cell to adapt to high osmolarity environments. The activation of this pathway is crucial for maintaining cellular functions and ensuring survival under osmotic stress (Morawska et al., 2022). 2.4 Heat and cold stress resistance B. subtilis adapts to temperature fluctuations by altering the structure and function of its spores. Spores produced at different temperatures exhibit variations in hydrophobicity, dipicolinic acid content, and resistance to heat and lysozyme. The protein CotH, which is heat-labile, plays a significant role in regulating spore coat formation at different temperatures, ensuring that spores are well-adapted to their environmental conditions (Isticato et al., 2019). The general stress response mediated by SigB also contributes to heat stress resistance by upregulating relevant stress response genes. 3 Sporulation inBacillus subtilis 3.1 Initiation of sporulation: environmental and nutritional signals Bacillus subtilis initiates sporulation in response to environmental stresses such as nutrient limitation. This process is a survival strategy that allows the bacterium to endure unfavorable conditions by forming highly resistant endospores (Wang and Zhang, 2024). The initiation of sporulation is tightly regulated by a network of signaling pathways that detect environmental and nutritional cues, triggering a cascade of genetic and biochemical events leading to spore formation. 3.2 Developmental stages of sporulation The sporulation process in Bacillus subtilis is a complex, multi-stage developmental pathway. It begins with the asymmetric division of the bacterial cell, resulting in a larger mother cell and a smaller forespore. This is followed by a series of morphological changes, including engulfment of the forespore by the mother cell, cortex formation, and the development of a protective spore coat. Each stage is meticulously regulated to ensure the proper formation of a dormant and resistant spore (Gu et al., 2018; Luu et al., 2022). 3.3 Role of sigma factors in sporulation 3.3.1σF, σE, σG, andσK in sequential sporulation stages Sigma factors are essential transcriptional regulators that control the expression of genes required at various stages of sporulation. In Bacillus subtilis, four main sigma factors—σF, σE, σG, and σK—play critical roles in the sequential progression of sporulation. σF is activated shortly after asymmetric division in the prespore and initiates the transcription of early sporulation genes. σE is activated in the mother cell following σF and controls the genes
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