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Bacteria move along gradients of chemical attractants. Two studies find that, in nutrient-rich environments, bacteria can grow rapidly by following a non-nutritious attractant -- but expanding too fast leaves them vulnerable. Growth strategies in bacteria moving by chemotaxis., Author(s): Henry Mattingly, Thierry Emonet Author Affiliations: A rule from bacteria to balance growth and expansion Bacteria can sense chemical attractants and use that information to navigate towards resources or [...]

The chemotaxis signalling network in Escherichia coli that controls the locomotion of bacteria is a classic model system for signal transduction (1,2). This pathway modulates the behaviour of flagellar motors to propel bacteria towards sources of chemical attractants. Although this system relaxes to a steady state in response to environmental changes, the signalling events within the chemotaxis network are noisy and cause large temporal variations of the motor behaviour even in the absence of stimulus (3). That the same signalling network governs both behavioural variability and cellular response raises the question of whether these two traits are independent. Here, we experimentally establish a fluctuation-response relationship in the chemotaxis system of living bacteria. Using this relationship, we demonstrate the possibility of inferring the cellular response from the behavioural variability measured before stimulus. In monitoring the pre- and post-stimulus switching behaviour of individual bacterial motors, we found that variability scales linearly with the response time for different functioning states of the cell. This study highlights that the fundamental relationship between fluctuation and response is not constrained to physical systems at thermodynamic equilibrium (4) but is extensible to living cells (5). Such a relationship not only implies that behavioural variability and cellular response can be coupled traits, but it also provides a general framework within which we can examine how the selection of a network design shapes this interdependence., It is standard procedure to characterize the stochastic dynamics of physical systems in thermodynamic equilibrium by measuring spontaneous fluctuations and responses to small external perturbations. Because these two distinct measurements [...]

Eukaryotic cells spatially organize mRNA processes such as translation and mRNA decay. Much less is clear in bacterial cells where the spatial distribution of mature mRNA remains ambiguous. Using a sensitive method based on quantitative fluorescence in situ hybridization, we show here that in Caulobacter crescentus and Escherichia coli, chromosomally expressed mRNAs largely display limited dispersion from their site of transcription during their lifetime. We estimate apparent diffusion coefficients at least two orders of magnitude lower than expected for freely diffusing mRNA, and provide evidence in C. crescentus that this mRNA localization restricts ribosomal mobility. Furthermore, C. crescentus RNase E appears associated with the DNA independently of its mRNA substrates. Collectively, our findings show that bacteria can spatially organize translation and, potentially, mRNA decay by using the chromosome layout as a template. This chromosome-centric organization has important implications for cellular physiology and for our understanding of gene expression in bacteria., In bacterial cells, the major mRNA species is the full-length transcript. Its predominance over nascent, partially transcribed mRNA is supported by northern blotting and recently by quantitative deep RNA sequencing [...]

Author(s): Ekaterina Korobkova [1, 4]; Thierry Emonet [1, 4]; Jose M. G. Vilar [2, 5]; Thomas S. Shimizu [3, 5]; Philippe Cluzel (corresponding author) [1] The chemotaxis network that governs [...]

The chemotaxis signalling network in Escherichia coli that controls the locomotion of bacteria is a classic model system for signal transduction. This pathway modulates the behaviour of flagellar motors to propel bacteria towards sources of chemical attractants. Although this system relaxes to a steady state in response to environmental changes, the signalling events within the chemotaxis network are noisy and cause large temporal variations of the motor behaviour even in the absence of stimulus. That the same signalling network governs both behavioural variability and cellular response raises the question of whether these two traits are independent. Here, we experimentally establish a fluctuation-response relationship in the chemotaxis system of living bacteria. Using this relationship, we demonstrate the possibility of inferring the cellular response from the behavioural variability measured before stimulus. In monitoring the pre- and post-stimulus switching behaviour of individual bacterial motors, we found that variability scales linearly with the response time for different functioning states of the cell. This study highlights that the fundamental relationship between fluctuation and response is not constrained to physical systems at thermodynamic equilibrium but is extensible to living cells. Such a relationship not only implies that behavioural variability and cellular response can be coupled traits, but it also provides a general framework within which we can examine how the selection of a network design shapes this interdependence. [ABSTRACT FROM AUTHOR]