arXiv subjects

Hélène de Maleprade

Publications and source records attributed to Hélène de Maleprade.

2 recordsLinked to original sources

arXiv2026

Hydrodynamics of microalgae in sea spray

Airborne transmission of biological matter is likely to cause numerous respiratory distress in coastal populations during certain harmful algal blooms. While we know that dissolved algal toxins aerosolize, the contribution of particle-associated toxins is still unknown. The observation of microalgae in the atmosphere suggests that cells or cell debris could be a carrier. Exchange of particulate matter between ocean and atmosphere is driven by sea spray: microplastics and bacteria aerosolize in jet droplets, following the bursting of air bubbles. However, current models for particle capture only consider surface effects, which fail to explain how large microalgal cells (5-50 um) can be entrapped in jet drops (100-800 um). Here, we demonstrate with a variety of species that microalgae are consistently captured in jet drops, and derive a new particle capture model based on the hydrodynamics of the jet. Using the enrichment factor, which measures the increase in concentration in the first jet drop relative to the bulk, we uncover two regimes. The transition between regimes strongly depends on cell size. In addition, we highlight the dynamics of particles within the jet and derive an enrichment model based on hydrodynamics rather than surface considerations. This work widens and generalizes established results on bacterial and microplastic entrapment in jet drops, resolving discrepancies found in the literature. Finally, we demonstrate that sea spray can aerosolize toxic Ostreopsis cf. ovata cells. This reveals a potential particulate pathway for airborne toxicity during harmful algal blooms and raises the question of the relative contribution of particles to that of dissolved toxins.

cond-mat.soft↗

arXiv2019

Motility and Phototaxis of $Gonium$, the Simplest Differentiated Colonial Alga

Green algae of the $Volvocine$ lineage, spanning from unicellular $Chlamydomonas$ to vastly larger $Volvox$, are models for the study of the evolution of multicellularity, flagellar dynamics, and developmental processes. Phototactic steering in these organisms occurs without a central nervous system, driven solely by the response of individual cells. All such algae spin about a body-fixed axis as they swim; directional photosensors on each cell thus receive periodic signals when that axis is not aligned with the light. The flagella of $Chlamydomonas$ and $Volvox$ both exhibit an adaptive response to such signals in a manner that allows for accurate phototaxis, but in the former the two flagella have distinct responses, while the thousands of flagella on the surface of spherical $Volvox$ colonies have essentially identical behaviour. The planar 16-cell species $Gonium~pectorale$ thus presents a conundrum, for its central 4 cells have a $Chlamydomonas$-like beat that provide propulsion normal to the plane, while its 12 peripheral cells generate rotation around the normal through a $Volvox$-like beat. Here, we combine experiment, theory, and computations to reveal how $Gonium$, perhaps the simplest differentiated colonial organism, achieves phototaxis. High-resolution cell tracking, particle image velocimetry of flagellar driven flows, and high-speed imaging of flagella on micropipette-held colonies show how, in the context of a recently introduced model for $Chlamydomonas$ phototaxis, an adaptive response of the peripheral cells alone leads to photo-reorientation of the entire colony. The analysis also highlights the importance of local variations in flagellar beat dynamics within a given colony, which can lead to enhanced reorientation dynamics.

cond-mat.soft↗