Measurement of the Low-Frequency Charge Noise of Bacteria

Abstract

Bacteria meticulously regulate their intracellular ion concentrations and create ionic concentration gradients across the bacterial membrane. These ionic concentration gradients provide free energy for many cellular processes and are maintained by transmembrane transport. Given the physical dimensions of a bacterium and the stochasticity in transmembrane transport, intracellular ion concentrations and hence the charge state of a bacterium are bound to fluctuate. Here, we investigate the charge noise of 100s of non-motile bacteria by combining electrical measurement techniques from condensed matter physics with microfluidics. In our experiments, bacteria in a microchannel generate charge density fluctuations in the embedding electrolyte due to random influx and efflux of ions. Detected as electrical resistance noise, these charge density fluctuations display a power spectral density proportional to $1/f^2$ for frequencies $0.05\mathrm{Hz}\le f\le 1\mathrm{Hz}$. Fits to a simple noise model suggest that the steady-state charge of a bacterium fluctuates by $\pm 1.30\times 10^{6}e(e\approx 1.60\times 10^{-19}\mathrm{C})$, indicating that bacterial ion homeostasis is highly dynamic and dominated by strong charge noise. The rms charge noise can then be used to estimate the fluctuations in the membrane potential; however, the estimates are unreliable due to our limited understanding of the intracellular concentration gradients.

arXiv commentMain article 24 pages, 12 figures, 1 table; supplementary 6 pages, 6 figure, 1 table

References in corpus (8)

• The physics of active polymers and filaments
• Active Membrane Fluctuations Studied by Micropipet Aspiration
• Effective Temperature of Red Blood Cell Membrane Fluctuations
• All-electrical monitoring of bacterial antibiotic susceptibility in a microfluidic device
• Resistance noise in electrically biased bilayer graphene
• Pink noise of ionic conductance through single artificial nanopores revisited
• On the emergence of very long time fluctuations and 1/f noise in ideal flows
• Noisy Transitional Flows in Imperfect Channels