Mechanisms and strategies for regulating sporulation and germination of Bacillus subtilis to enhance probiotic effects

Abstract

Bacillus subtilis microecological agents are promising feed additives to replace antibiotics in the livestock, poultry, and aquaculture industries. B. subtilis cells can form spores that are highly resistant to harsh conditions, including heat, radiation, mechanical force, and acidic stomach environment. Spore yield determines the probiotic effects significantly. Sporulation can be initiated under high cell density and nutrient starvation. In turn, the spores can germinate when given a specific germinant stimulus, such as amino acids and high pressure. To date, the underlying mechanisms of B. subtilis sporulation and germination remain incomplete, and the strategies for improving spore yield and triggering spore germination need further improvement. Understanding the interconversion of B. subtilis spores and vegetative cells is pivotal for improving the titer of microecological agents. Therefore, the mechanisms of B. subtilis sporulation and spore germination (e.g., spo0A expression, phosphorylation, sigma factors regulation, and germinant stimuli) are systematically summarized in the present study. Meanwhile, mechanism-based approaches, such as lignocellulosic medium pretreatment, fermentation, desiccation, and high-pressure stimulus, that promote the transformation between spores and vegetative cells are presented. Furthermore, the mechanisms of sporulation environment and spores’ structure determining spores’ resistance are discussed. Finally, the application of B. subtilis microecological agents in animal husbandry is summarized and the perspectives for the next-generation microecological agents are proposed to enhance value-added utilization of lignocellulosic biomass and animal health. Overall, with the revelation of B. subtilis sporulation and germination mechanisms and the development of advanced strategies to enhance spore yield, the probiotic effects of B. subtilis microecological agents will be further improved, thereby promoting food safety and valorization of lignocellulosic biomass.