Microfluidics for evolutionary biology

G. L. MIÑO; J. SPARACINO; M. G. REYES; J. A. SÁNCHEZ; P. A. PURY; A. J. BANCHIO; V. I. MARCONI

Rio de Janeiro

Conferencia; VIII Workshop in Microfluidics / I Brazil-Argentina Microfluidics; 2018

Pontificia Universidad Católica de Río de Janeiro

The choanoflagellates are a group of free-living unicellular and colonial flagellate eukaryotes considered to be the closest living relatives of the animals, their sister group. The changes in gene content that preceded the origin of animals can be reconstructed by comparison with them. Choanoflagellates Salpingoeca rosetta, under suitable environmental cues can differentiate into two types of solitary cells. Each group is recognized by its own swimming strategy and its body size: fast and small or slow and large. Under nutrient limited conditions, S. rosetta experience a haploid-to-diploid transition, evidenced by the presence of gametes. It is challenging to determine if there is a connection between the two types of cells and the male and female gametes. Here is where microfluidics can play an important role in evolutionary biology, if it helps to isolate and concentrate the fast cells because under laboratory conditions always they are mixed populations. Motivated with this current interest, we have measured their sizes and characterized their motilities, developing a new soft for automatic tracking analysis of big amount of data [Sánchez et al, 2016, ReyesThesis2017, ReyesPreprint2018]. We find that fast cells swim remarkably different from slow cells, being their trajectories quasi-straight and interrupted by changes of direction while the latter are strongly tortuous. We propose a phenomenological model to reproduce the observed choanoflagellate dynamics. Further, cells are confined into a flat device divided by a wall of asymmetric obstacles separated by micro-gaps. A systematic study of the directed transport is performed in order to optimize the device geometry. We solve the Langevin dynamical equations of motion using the experimental parameters. Simulations show that fast choanoflagellates are remarkably easier to be directed efficiently for a wide range of wall geometries, while slow cells are hardly directed independently of the geometry due to their tortuous swimming behavior. As a consequence, a rigorous characterization of each micro-swimmer motility is crucial for a proper micro-device optimization, using the largest amount of data available, and automatically. Even more, due to the clear differences between fast and slow choanoflagellates rectification results, an efficient micro-sorter device was fabricated, obtaining a good agreement between theory and experiments [Miño et al, preprint].