Single-Cell Analysis of the Dps Response to Oxidative Stress

Abstract

Microorganisms have developed an elaborate spectrum of mechanisms to respond and adapt to environmental stress conditions. Among these is the expression of dps, coding for the DNA-binding protein from starved cells. Dps becomes the dominant nucleoid-organizing protein in stationary-phase Escherichia coli cells and is required for robust survival under stress conditions, including carbon or nitrogen starvation, oxidative stress, metal exposure, and irradiation. To study the complex regulation of Dps in E. coli, we utilized time-lapse fluorescence microscopy imaging to examine the kinetics, input encoding, and variability of the Dps response in single cells. In the presence of an oxidative stressor, we observed a single pulse of activation of Dps production. Bacteria encounter many stresses during their development, and they need to be able to adapt quickly to the environment to survive. Bacterial response mechanisms frequently involve specific sets of genes that are activated to help the cell adapt to stress. Alternative sigma factors, of which Escherichia coli has seven, are a frequently used regulatory mechanism (1). While housekeeping genes expressed during exponential growth are controlled by the transcription factor 70 (2, 3), alternative sigma factors act as transcription initiation factors to control the activation of specialized regulons under specific growth or stress conditions (4). The general stress response sigma factor S activates the transcription of Ͼ70 genes, conferring resistance to carbon/phosphate/nitrogen starvation, heat shock, high/low pH, UV radiation, and oxidative stress, among others (5, 6).Microorganisms living in an aerobic environment unavoidably encounter oxidative stress as a by-product of their aerobic metabolism (7). The resultant formation of reactive oxygen species (ROS) can lead to damage to cellular components, including membranes, DNA, and proteins (8). As an adaptation to this condition, bacteria produce enzymes, such as superoxide dismutases and reductases, to scavenge these toxic components (9). Additionally, cells also face external sources of oxidative stress: macrophages produce superoxide and nitric oxide to kill invading bacteria (10), following perception of pathogens, plants also induce the synthesis of organic peroxides (11), certain communities of microorganisms excrete ROS to inhibit the growth of their competitors (12), and exposure to environmental redox cycling compounds can cause damaging intracellular redox reactions (13).In this challenging environment, bacteria have developed refined molecular mechanisms of defense. The DNA-binding protein from starved cells (Dps) plays a crucial role during stress exposure. Escherichia coli dps mutants experience a severe reduction in survival when exposed to any of several different stressors, including oxidative stress, heat shock, metal exposure, UV and gamma irradiation, or extreme pH (14-16). Additionally, Dps was shown to protect cells against DNA strand breakage (17). In E. coli, the protective effect of...

Dissecting the structural and functional roles of a putative metal entry site in encapsulated ferritins

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“…Recent studies of stochastic gene expression are supportive of the intriguing possibility of metabolic heterogeneity. For example, studies found that genetically identical cells in the same environment may produce different amounts of metabolically relevant proteins [28][29][30][31]. Recent computational work suggested that such different protein expression could give rise to metabolic heterogeneity in E. coli cells [32].…”

Draft Genome Sequences of Acinetobacter and Bacillus Strains Isolated from Spacecraft-Associated Surfaces

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