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Spore-forming bacteria mainly belong to two genera of the Firmicutes phylum, the aerobic or facultative anaerobic Bacilli and the strictly anaerobic Clostridia . These organisms share the ability to undergo a complex developmental cell differentiation process that allows them to adapt to harsh environmental conditions by producing highly resistant endospores (spores). The process of spore formation, sporulation, involves progression through different stages including commitment to sporulation, chromosome segregation, sporulation-specific cell division, differential gene expression and specific signal transduction mechanisms. At the end of the process, a mature, highly resistant and quiescent spore is formed. The dormant spores can survive indefinitely in the absence of water and nutrients, surviving extremes of temperature and pH and to the exposure to UV and noxious chemicals. When the environmental conditions return favourable to cell growth, the spore germinates originating a new vegetative cell able to grow, duplicate and eventually to sporulate again. Spores are ubiquitous in nature. They can be isolated from soils and aquatic samples, including samples from extremes environments such as deserts, hydrothermal sites and artic ices. Spores are also found associated with other organisms, including insects, plants and animals, and have been shown able to carry out their entire life cycle, including germination-growth-sporulation, within the animal host. Dissemination in a variety of environments is due to the stability and resistance properties of the spore, which in turn is due to the peculiar structure of the spore. The spore chromosome is protected by specific DNA-binding proteins (small acid soluble proteins) and is contained within a dehydrated cytoplasm (core), which is surrounded by several protective layers: a thick peptidoglycan-like cortex, a multilayered, proteinaceous coat and, in some species, an exosporium formed of proteins and glycans. Although metabolically quiescent, the …
Cutting et al. (Thu,) studied this question.