From soil bacteria to sperm swimming in the fallopian tubes, microorganisms are often found to swim within confined environments. What is the effect of confinement on their flow fields? In a new paper, recently published in Physical Review Letters, we combine experiment and modelling to show that -contrary to expectations- the variety of microbial flow fields is greatly increased under confinement. This can in turn have have qualitative effects on both the biology (e.g., feeding currents) and the physics (e.g., collective behaviour) of microorganisms in confinement. This work was done in collaboration with Raphael Jeanneret and Mitya Pushkin.
Many swimming microorganisms respond to light stimuli. Can we then use light to change the behaviour of a whole population and “order” the suspension to mix itself? Discover it in our new work, just accepted for publication in Physical Review Letters. A collaboration with our friends at IMEDEA (Link to be added asap. In the meantime you can access the Arxiv version).
How do cilia synchronise? Through hydrodynamics? Elasticity? Intracellular coupling? The mechanism seems to depend on whether these oscillators belong to same cell or not. In the latter case, we have shown that hydrodynamic interactions suffice; in the former, however, direct intracellular coupling between the flagella is necessary (see here, here, and here). How is this coupling acting? How can it promote opposite types of synchronisation? Our idea is that synchronisation states depend on the cell actively stiffening/relaxing the internal fibres joining the ciliary basal bodies. We explore this hypothesis in our new paper, recently accepted in J. Roy. Soc. Interface, looking at a minimal model of “cilia coupled by intracellular connections”. (ArXiv preprint. Full version and Supplementary Informations including animations). A big Thank to U. Melbourne and its Department of Mathematics and Statistics for hosting Marco during the final developments of this work!!
We’re delighted to share the news that we have received travel funds from the EPSRC Network Plus Emergence and Physics Far From Equilibrium to kickstart a collaboration with the groups of Dr. Giorgio Volpe (UCL, UK), Dr. Nuno Araújo (U. Lisbon, Portugal) and Dr. Idan Tuval (IMEDEA-UIB, Spain). The project, which will start later this year, focusses on understanding and controlling transport properties of binary suspensions where microscopic active particles interact with passive ones (cargoes).
Phototaxis is one of the main categories of motility regulation by microorganisms. Arguably, it is particularly important for motile micro algae, due to their photosynthetic activity. One of the organisms where it has been studied the most is our beloved micro alga Chlamydomonas reinhardtii. Currently, we have a pretty good idea of the mechanism leading the cells to reorient towards/away from the light, but not much is known about what happens after they’ve reoriented…. In our recent paper we start looking into this, with surprising results.
Does a stronger interaction always make for a more stable system? Certainly not for synchronising oscillators, as we show in a paper just accepted in Physical Review Fluids. There we study the behaviour of a strip of colloidal rotors as the system is lifted from a no-slip surface. As the hydrodynamic coupling strengthens, the system develop recurring phase defects which worsen its synchronisation. Our simulations show that defects result from a competition between short-range and long-range coupling. The paper is currently accessible through the ArXiv.
Update: The paper has been published (open access) and is now available here.
Our brief introduction to Chlamydomonas reinhardtii -aimed at physicists- is published in by the European Physical Journal as part of a Special Topics Issue on Microswimmers.
Particle entrainment by Raphaël, just accepted on Nat Com!
What happens to passive microparticles within a suspension of microorganisms? If the particles are small, they can be entrained over large distances by the micro swimmers. These interactions are rare, but their magnitude is large and -as it turns out- they end up dominating particle dynamics, which now resembles a jump-diffusion process. This is presented and discussed in details in a new work led by Raphaël, just accepted on Nature Communications. A preprint of the article (well.. a previous version) is currently available on the Arxiv.
Update. The article is now available here.
Together with Idan Tuval, I have been recently working on a Viewpoint for Physics, about an interesting recent PRL publication by Greta Quaranta, Marie-Eve Aubin Tam and Daniel Tam, from the University of Delft. They proved that flagellar synchronisation in Chlamydomonas depends on the presence of striated fibres joining the basal bodies of the two flagella. Apparenly, synchronisation of flagella from different cells or from the same cell can be based on completely different mechanisms! This is a really nice work, which opens a lot of new questions…