Time-frequency rheology of living systems – RHEOLIFE

Morse wavelets and more generally analytic complex wavelets have been tested on model (numerical) and real physiological signals, offering a generalisation of this approach to signals of very different nature (physiological signals recorded from whole organs, signals collected by local probes on single cells or group of cells).

The experiments of AFM on single yeast cells have been markedly improved, by testing and validating a first protocol for sample surface treatments for the immobilization of yeast cells prior to local indentation experiments.

New time-frequency cross-correlation and intercorrelation functions, based on these analytical wavelets were defined and validated as efficient for deciphering the distribution of frequency ratios (rational, irrational, lack of ratios) of non stationary signals. The impact of additive of multiplicative noise on these distributions and their stability in time will be a further challenge that will be tackled in the near future

The experimental demonstration of the possibility to extract the Young's module at low indentation speeds of the AFM cantilever was achieved and numerical codes where written to indentify the different regimes of indentation and delimit the indentation range where the cell wall remains elastic (regime of very small deformation). This work is strongly supported by the recent development of Task 1 (see text). Preliminary tests on creep and relaxation experiments on leaving yeast cells have also been performed and will be repeated in the next months, to validate the observed mechanical regimes and adapt the analysis (numerical) programs for large data sets.

In summary, we have demonstrated the feasibility and reproducibility of single yeast cell mechanical measurements and their condition of operations in exponential growth conditions. Different cell lines or culture conditions have been tested with biochemical methods that modulate the cell energetic metabolism. Analytical and modeling tools have been implemented to model these cell wall mechanics and include their non-stationarity during the experiments.
In addition, we have independently developed an original time-frequency analytico-modeling of complex physiological (mechanical, rheological, electrical, optical) signals to decipher underlying rhythms from stochastic (noise) response. This method will be tested on creep response signals from living yeast cells. Analytical and numerical modeling of the mechanical response of walled-objects (such as yeast cells) has also be initiated, based on finite element methods.

1. S. Dupont, F. Argoul, E. Gerasimova-Chechkina, M.R. Irvine & A. Arneodo, Experimental evidence of a phase transition in the multifractal spectra of turbulent temperature ?uctuations at a forest canopy top, accepté pour publication au J. of Fluid Mechanics (2020)
2. S. Polizzi, A. Arneodo & F. Argoul, Emergence of log-normal distributions in avalanche processes in living systems, in preparation, to be submitted in the fall 2020
3. C.L. Bouchez; N. Hammad; S. Cuvellier; S. Ransac; M.Rigoulet; A. Devin, The Warburg effect in Yeast: Repression of mitochondrial metabolism is not a prerequisite to promote cell proliferation Frontiers (2020) in press
4. M. Scherlinger, A. Devin, S. Ransac, J. Lykkesfeldt, B.Marteyn Ascorbate maintains a low plasma oxygen level. Louise Injarabian,. Scientific Reports (2020) in press
5. C.L Bouchez; E. D Yoboue; L.E de la Rosa Vargas; B. Salin S. Cuvellier;M. Rigoulet; S. Duvezin-Caubet; A. Devin.“Labile” heme critically regulates mitochondrial biogenesis through the transcriptional co-activator Hap4p in Saccharomyces cerevisiae. Journal of Biological Chemistry (2020) in press
6. J.Y. Tinevez, E.T. Arena, M. Anderson, G. Nigro, L.Injarabian, A. André, M. Ferrari, A. Devin, S.L. Shorte, P.J. Sansonetti, B.S. Marteyn. Shigella-mediated oxygen depletion is essential for intestinal mucosa colonization. Nature microbiology 4, 2001-2009 (2019)
7. N. Sharikadze N. Hammad, C. Bouchez, N. Averet, M. Rigoulet, E. Zhuravliova, D. G Mikeladze, A. Devin, Inhibition of mitochondrial cytochrome c oxidase by metabolized Nobiletin in yeast. Journal of biological regulators & Homeostatic Agents 33(4) 1097-1103 (2019).
8. A. Guillet, A. Arneodo, P. Argoul & F. Argoul, Quantifying the rationality of rhythmic signals, in preparation – to be submitted in july 2020