![]() The level of Spo0A~P is tightly regulated through a phosphorelay system. Indeed, the level of Spo0A~P increases gradually as the cell enters the stationary phase ( Fujita and Losick, 2005). Spore development is initiated when the cellular level of Spo0A~P reaches the threshold level ( Fujita et al., 2005). subtilis, the entry into sporulation is subject to bistability ( Veening et al., 2005), which is regulated by the expression and phosphorylation level of the transcription factor and response regulator Spo0A~P ( Hoch, 1993). This heterogeneity is in part due to the bistable expression/activation (“ON” or “OFF”) states of regulatory proteins ( Dubnau and Losick, 2006). subtilis cells grown to stationary phase are heterogenic as they display a multitude of cell types associated with distinct differentiation pathways ( Kearns and Losick, 2005). The latter cell subsequently engulfs the forespore (stages II–III), ensures its proper development to the endospore, and finally undergoes autolysis releasing a mature spore (stage VII) ( Errington, 1993, 2003 Stragier and Losick, 1996 Eijlander et al., 2014).ī. The process initially involves asymmetric cell division near one of the cell poles, which results in the formation of a smaller cell, the prespore or forespore, and a larger cell, the mother cell (stages I–II). Numerous genes are up- or down-regulated or even switched on or off in the process of endospore formation. The model organism, Bacillus subtilis, is to date the best-studied organism in terms of spore development. This highly resistant form of bacteria can survive harsh conditions that are usually lethal to their vegetative counterparts. In response to nutrient deprivation, some bacterial species within the Firmicutes phylum differentiate into dormant and non-reproductive cells called endospores. Based on these findings, I suggest to name the here described cell type as “dwarf cells” to distinguish them from the well-known minicells observed in mutants defective in septum placement or proper chromosome partitioning. This work reveals that the continuation of asymmetric cell division, which results in the formation of the small round cells, is a way for cells to delay or escape from-unsuccessful-sporulation. These data suggest that in minimal media, many cells are able to initiate but fail to complete spore development, and therefore return to normal growth as rods. In most cases observed, the small round cells arise in the presence of sigma H but absence of sigma F activity, different from cases of abortive sporulation described for rich media. In contrast to wild-type cells, mutants harboring spo0A or spoIIIE/ sftA double mutations neither sporulate nor produce this special cell type, providing evidence that the small round cells emerge from the abortion of endospore formation. subtilis undergoes an asymmetric cell division that produces small and round-shaped, DNA containing cells. Here, I show that during prolonged growth during stationary phase in minimal medium, B. However, spore development of the model organism Bacillus subtilis has mainly been studied by means of media or conditions optimized for the induction of sporogenesis. Sporulation is the most enduring survival strategy developed by several bacterial species. Division of Infectious Diseases, University Medical Center Freiburg, Freiburg, Germany.
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