Modeling and Controlling choanoaflagellates transport with asymmetric micro-constrictions.

J. SPARACINO; G. L. MIÑO; M. A. R. KOEHL; N. KING; R. STOCKER; A. J. BANCHIO; V. I. MARCONI

Bonn

Workshop; Jülich Soft Matter Days 2015; 2015

Forschungszentrum Jülich GmbH Institute of Complex Systems, ICS-3

In evolutionary biology choanoflagellates are broadly investigated as the closest living relativesof the animal ancestors. Under diverse environmental cues, choanoflagellate Salpingoecarosetta can differentiate in two types of solitary cells with different swimming strategy and size:(i) slow and large and (ii) fast and small. It is known that under nutrient limiting conditions,they experience an haploid-to-diploid transition, evidenced by the presence of gametes. It isinteresting to determine if there is a connection between the two types of cells and the male andfemale gametes.In order to efficiently direct choanoflagellates we have measured their motilities to determinethe relevant parameters to describe the cell dynamics.We present a phenomenological 2D?model for the choanoflagellate dynamics under microconfinementinto a flat device divided by a wall of asymmetric obstacles separated by microopenings.To optimize the geometry of the obstacle wall for directing the cell populations, wesystematically study the directed transport efficiency by solving our set of dynamical equationsusing Langevin dynamics, with experimental parameters for the cell motilities and sizes. Theslow cells swim remarkably different from the fast cells, being their trajectories strongly tortuous.As a consequence, the fast choanoflagellates are more efficiently directed for a widerange of obstacle wall geometries while the slow cells are harder to direct, independently of thegeometry. For both populations, narrower openings of similar size to the cell dimension, aremore efficient rectifiers as well as devices with greater obstacle?s radii. These results could becounterintuitive, but are understood for the observed specific cells swimming along walls: fastcells with straight tracks are able to take advantage of the device geometry to be directed, inopposite to the slow cells with a more Brownian strategy to swim.Based on our observations and predictions for separated populations, we conclude that it isimportant to characterize rigorously as a first step each microswimmer motility in order tocontrol them. Even more, due to the clear differences between fast and slow choanoflagellatesrectification results, an efficient sorter device of mixed populations could be designed for furtherapplication in evolutionary biology.