Phenotyping single-cell motility in microfluidic confinement

Abstract

The movement trajectories of organisms serve as dynamic read-outs of their behaviour and physiology. For microorganisms this can be difficult to resolve due to their small size and fast movement. Here, we devise a novel droplet microfluidics assay to encapsulate single micron-sized algae inside closed arenas, enabling ultralong high-speed tracking of the same cell. Comparing two model species - Chlamydomonas reinhardtii (freshwater, 2 cilia), and Pyramimonas octopus (marine, 8 cilia), we detail their highly-stereotyped yet contrasting swimming behaviours and environmental interactions. By measuring the rates and probabilities with which cells transition between a trio of motility states (smooth-forward swimming, quiescence, tumbling or excitable backward swimming), we reconstruct the control network that underlies this gait switching dynamics. A simplified model of cell-roaming in circular confinement reproduces the observed long-term behaviours and spatial fluxes, including novel boundary circulation behaviour. Finally, we establish an assay in which pairs of droplets are fused on demand, one containing a trapped cell with another containing a chemical that perturbs cellular excitability, to reveal how aneural microorganisms adapt their locomotor patterns in real-time.

Interaction of the mechanosensitive microswimmer Paramecium with obstacles

“…It is therefore critical to understand how their foraging efficiency depends on their local interactions with obstacles found in their natural habitat. In order to answer these questions, a large array of literature has been dedicated to the study of motility in engineered complex environments in the past years [ 17 , 20 , 21 , 31 ].…”

Learning dynamical models of single and collective cell migration: a review

“…Using clustering and dimensional reduction, this matrix leads to a low-dimensional behaviour space revealing two-state 'roaming and dwelling' model of swimming behaviour for multi-ciliate Tetrahymena cells. Conceptually similar approaches have been developed for other organisms and their interactions with confining boundaries [191], revealing different types of discrete cell states including run-tumble-stop behaviour in biflagellate vs run-shock-stop behaviours in octoflagellate protozoans (figure 7(B)). These analysis frameworks could have potential also for eukaryotic cell migration, provided that a sufficient time-resolution can be achieved experimentally, which is key for a sufficient sampling of the sliding time windows of such an approach.…”

“…• Temporal variability: the behaviour of cells may also exhibit variations over time: as cells undergo the cell cycle, they grow, which may also affect other behaviours, including cell migration [188]. Furthermore, cells may switch between qualitatively distinct modes of behaviour, meaning that separate models for each behaviour, as well as a model for the switching itself, must be considered [189][190][191]. • Environmental variability: potentially unobserved changes in the extra-cellular environment may cause changes in behaviour, which could be mistaken for other types of variability.…”

Biophysical Fluid Dynamics in a Petri Dish

“…when studying Liesegang rings [3,4]) or in entomology where they are convenient enclosures to study the behaviour of insects and small animals [5,6]. A Petri dish environment is also a simple and common setting in which to examine the locomotion of swimming organisms, particularly those whose body size is tens of microns to millimetres [7][8][9][10][11].…”