Abstract
Bacteria use a variety of stress-sensing systems to sense and respond to diverse stressors and to ensure their survival under adverse conditions. The gram-positive bacterium Bacillus subtilis responds to energy stress (ATP depletion) and to environmental stressors using two distinct stress-sensing pathways that converge on the alternative sigma factor σB to provoke a general stress response. Past efforts to study the σB stress response in bulk culture and on agarose pads were unable to visualize the responses of individual cells under tightly controlled conditions for extended periods of time. Here we use a microfluidics-based strategy to discern the basic features of σB activation in single cells in response to energy and environmental stress, both immediately upon stressor exposure and for tens of generations thereafter. Upon energy stress at various levels of stressor, cells exhibited fast, transient, and amplitude-modulated responses but not frequency modulation as previously reported. Upon environmental stress, which is mediated by the stressosome complex, wild-type cells primarily exhibited a transient and amplitude-modulated response. However, mutant cells producing only one of the four paralogous RsbR stressosome proteins showed striking and previously unseen differences. Whereas RsbRA-only cells mimicked the wild type, RsbRC-only cells displayed a slower but sustained overall response composed of repeated activation events in single cells.
Highlights
Microorganisms respond to stressful conditions by activating genes that facilitate cell survival
Because bacteria are often subjected to rapidly changing conditions in nature, they have evolved stressresponse mechanisms that are poised to respond to harsh environmental conditions
Many of the proteins that mediate bacterial stress responses are known, but technical limitations have made it difficult to discern how individual cells respond to stress at short and long time scales
Summary
Microorganisms respond to stressful conditions by activating genes that facilitate cell survival. These stress responses often involve the activation of an alternative sigma factor, such as in Escherichia coli the heat shock factor σ32, the cell envelope stress factor σE, and the general stress-response factor σS [1, 2]. Under non-stress conditions, σB is held inactive by the anti-sigma factor RsbW, which binds to σB and prevents it from binding to RNA polymerase (Fig 1) [5]. The anti-anti-sigma factor RsbV binds to RsbW, thereby freeing σB to bind to RNA polymerase and activate stress-response genes [6,7,8]. ΣB activity responds to relatively low levels of stress that have minimal effects on cell growth, σB has an important role in cell survival at higher stress levels [11, 12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
