24 research outputs found
Paradoxical enhancement of chemoreceptor detection sensitivity by a sensory adaptation enzyme
A sensory adaptation system that tunes chemoreceptor sensitivity enables motile Escherichia coli cells to track chemical gradients with high sensitivity over a wide dynamic range. Sensory adaptation involves feedback control of covalent receptor modifications by two enzymes: CheR, a methyltransferase, and CheB, a methylesterase. This study describes a CheR function that opposes the signaling consequences of its catalytic activity. In the presence of CheR, a variety of mutant serine chemoreceptors displayed up to 40-fold enhanced detection sensitivity to chemoeffector stimuli. This response enhancement effect did not require the known catalytic activity of CheR, but did involve a binding interaction between CheR and receptor molecules. Response enhancement was maximal at low CheR:receptor stoichiometry and quantitative analyses argued against a reversible binding interaction that simply shifts the ON-OFF equilibrium of receptor signaling complexes. Rather, a short-lived CheR binding interaction appears to promote a long-lasting change in receptor molecules, either a covalent modification or conformation that enhances their response to attractant ligands
Experimental Generation of Spin-Photon Entanglement in Silicon Carbide
A solid-state approach for quantum networks is advantages, as it allows the
integration of nanophotonics to enhance the photon emission and the utilization
of weakly coupled nuclear spins for long-lived storage. Silicon carbide,
specifically point defects within it, shows great promise in this regard due to
the easy of availability and well-established nanofabrication techniques.
Despite of remarkable progresses made, achieving spin-photon entanglement
remains a crucial aspect to be realized. In this paper, we experimentally
generate entanglement between a silicon vacancy defect in silicon carbide and a
scattered single photon in the zero-phonon line. The spin state is measured by
detecting photons scattered in the phonon sideband. The photonic qubit is
encoded in the time-bin degree-of-freedom and measured using an unbalanced
Mach-Zehnder interferometer. Photonic correlations not only reveal the quality
of the entanglement but also verify the deterministic nature of the
entanglement creation process. By harnessing two pairs of such spin-photon
entanglement, it becomes straightforward to entangle remote quantum nodes at
long distance.Comment: 8 pages in total, 4 figures in the main text, 1 figure in the
supplemental materia
Robust estimation of bacterial cell count from optical density
Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data
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Paradoxical enhancement of chemoreceptor detection sensitivity by a sensory adaptation enzyme.
A sensory adaptation system that tunes chemoreceptor sensitivity enables motile Escherichia coli cells to track chemical gradients with high sensitivity over a wide dynamic range. Sensory adaptation involves feedback control of covalent receptor modifications by two enzymes: CheR, a methyltransferase, and CheB, a methylesterase. This study describes a CheR function that opposes the signaling consequences of its catalytic activity. In the presence of CheR, a variety of mutant serine chemoreceptors displayed up to 40-fold enhanced detection sensitivity to chemoeffector stimuli. This response enhancement effect did not require the known catalytic activity of CheR, but did involve a binding interaction between CheR and receptor molecules. Response enhancement was maximal at low CheR:receptor stoichiometry and quantitative analyses argued against a reversible binding interaction that simply shifts the ON-OFF equilibrium of receptor signaling complexes. Rather, a short-lived CheR binding interaction appears to promote a long-lasting change in receptor molecules, either a covalent modification or conformation that enhances their response to attractant ligands