Micro-swimmer dynamics in self-organized phases of helical biopolymers

Envoyé par Eric Grelet 
Micro-swimmer dynamics in self-organized phases of helical biopolymers
vendredi 12 mai 2023 17:19:06
Open PhD position at Paul Pascal Research Center (http://www.crpp.cnrs.fr), a multidisciplinary research laboratory belonging to French National Center for Scientific Research (CNRS) and to the University of Bordeaux (UB).

Research Project:
Micro-swimmer dynamics in self-organized phases of helical biopolymers

Active systems are formed by elementary units capable of exploiting the surrounding environment to produce directed motion. They are intrinsically non-equilibrium systems for which specific original collective behaviors have emerged. This is the case, for example, at the macroscopic scale of schools of fish or flocks of birds.
At the microscopic scale, bacteria are a model system of active particles and their movement in complex fluids constitutes a common biological situation, especially during infection processes. Specifically, we are interested in the interaction between bacteria with flagella (e.g. Escherichia Coli, Bacillus Subtilis) and self-organized phases of biopolymers. Preliminary results from our group have shown not only the possibility of tuning the swimming orientation of the bacteria, but also of modulating the swimming speed [1], a mechanism resulting from the interaction between the propulsive bacteria flagella (See figure) and the self-organized surrounding matrix.
In this context, we aim at studying the influence of shape and helicity of the particles forming the complex fluids by using helical biopolymers. One original choice is the bacterial flagella themselves, for which an entirely original self-organization has been demonstrated [2].
The objective of the PhD project is to study the interaction between biological micro-swimmers and a suspension composed of helical biopolymers morphologically similar to the flagella of bacteria. A first part will consist in understanding the self-assembly of these chiral particles in particular in dense regimes and in characterizing their dynamics (such as the determination of their anisotropic diffusion coefficients) by single particle tracking. In a second part of the project, we will introduce bacterial micro-swimmers into these novel self-organized phases, in order to understand the hydrodynamic interactions between the bacteria and the surrounding complex fluid. Our experimental system enables direct visualization by optical microscopy of the different components thanks to orthogonal fluorescence labeling, so that a quantitative characterization of their structural and dynamic behavior, such as the speed of micro-swimmers, can be performed.
[1] L. Alexander, Bacterial microswimmers as active particles in colloidal liquid crystals, Thèse, Université de Bordeaux 2021.
[2] E. Barry et al., Entropy-driven formation of a chiral liquid-crystalline phase of helical filaments, Phys Rev Lett. 2006, 96:018305.

Your Profile: This PhD project is mainly experimental with international for physics modelling. It is fundamentally interdisciplinary, combining soft matter physics, physico-chemistry, as well as the production and manipulation of biological objects. The candidates should be in possession of, or expect to attain, a Master’s in a relevant discipline (Physical Chemistry, Materials science, Physics, Nanoscience, etc). Good skills in written and oral communication in English are important.

Applications should include a CV, contacts of two referees and a brief statement of interests for this specific PhD research project. Please send your application or any inquiry, to eric.grelet@crpp.cnrs.fr.
More information: Prof. Eric Grelet
CRPP, CNRS & University of Bordeaux, 115 av Schweitzer, 33600 Pessac, France
Phone: +33 5 56 84 56 13 Fax: +33 5 56 84 56 00 [www.crpp.cnrs.fr]