Bistability in the Bacillus subtilis K‐state (competence) system requires a positive feedback loop

Abstract

SummaryHigh expression of the transcriptional activator ComK occurs in 10-20% of the cells in stationary phase cultures of Bacillus subtilis strain 168. ComK drives the expression of more than 100 genes constituting the semidormant K-state, distinct from sporulation and vegetative growth. Among the genes so activated are those that permit competence for genetic transformation. We have addressed the origin of bistability in expression of ComK. We show that bistability requires positive autoregulation at the promoter of comK , but not a potential toggle switch, in which ComK represses the promoter of rok and Rok represses the promoter of comK . We further address the source of the noise that results in the stochastic selection of cells that will express comK . A revised model for the regulation of comK expression is proposed that partially explains bistability.

Regulation of Type IV Secretion Apparatus Genes during Ehrlichia chaffeensis Intracellular Development by a Previously Unidentified Protein

“…The expression of ecxR was autoregulated, like many other transcription factors (20,29,30), in response to an unknown signal. The mechanism of the downregulation of the virBD genes has not been determined yet.…”

Gene transcription from the linear plasmid pBClin15 leads to cell lysis and extracellular DNA-dependent aggregation of Bacillus cereus ATCC 14579 in response to quinolone-induced stress

“…It has been shown that phenotypical divergence of cells in a clonal population of bacteria may arise due to stochastic processes. This bistability phenomenon has, for example, been observed in B. subtilis for relevant phenotypes such as sporulation, competence, motility and biofilm formation (Chai et al, 2008;Kearns et al, 2004;Lopez et al, 2009;Maamar & Dubnau, 2005;Veening et al, 2005). In addition, it is believed that persister cells, a subpopulation of normally susceptible bacteria that are non-inherently more tolerant to stress, may arise due to random processes (Balaban et al, 2004;Lewis, 2007;Shah et al, 2006).…”

Transcription factor levels enable metabolic diversification of single cells of environmental bacteria

“…In this scenario, there is a transition from a single gene expression state to two different stable states driven by a change in substrate. In all these cases, the presence of positive feedback is required to generate and maintain the different expression states (Acar et al, 2005;Maamar and Dubnau, 2005;Suel et al, 2006;Veening et al, 2008;Kotte et al, 2014;Gallie et al, 2015;Venturelli et al, 2015), while molecular noise may enable phenotype switching. The existence of two simultaneous expression states without positive feedback is a much less-frequent phenomenon, and to the best of our knowledge has never been observed in this context.…”