Mar 25, 2020

Flagellar dynamics reveal large fluctuations and kinetic limit in the Escherichia coli chemotaxis network

BioRxiv : the Preprint Server for Biology
R. BanoYann R Chemla


Biochemical signaling networks allow living cells to adapt to a changing environment, but these networks must cope with unavoidable number fluctuations ("noise") in their molecular constituents. Escherichia coli chemotaxis, by which bacteria modulate their random run/tumble swimming pattern to navigate their environment, is a paradigm for the role of noise in cell signaling. The key signaling protein, CheY, when activated by (reversible) phosphorylation, causes a switch in the rotational direction of the flagellar motors propelling the cell, leading to tumbling. CheY-P concentration, [CheY-P], is thus a measure of the chemotaxis networks output, and temporal fluctuations in [CheY-P] provide a proxy for network noise. However, measuring these fluctuations in the single cell, at the relevant timescale of individual run and tumble events, remains a challenge. Here we quantify the short-timescale (0.5-5 s) fluctuations in [CheY-P] from the switching dynamics of individual flagella, observed using time-resolved fluorescence microscopy of optically trapped E. coli cells. This approach reveals large [CheY-P] fluctuations at steady state, which may play a critical role in driving flagellar switching and cell tumbling. A stochastic theo...Continue Reading

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