Pair-wise interactions between Chlamydomonas Reinhardtii: A numerical and experimental study *

Physical interactions between motile micro-organisms give rise to complex dynamics and collective motion. A better understanding of these interactions is crucial to explain the emergence of coherent motion involved in many biological phenomena from reproduction to biofilm formation. Numerical and analytical methods have been used extensively to study pair-wise interactions of micro-organisms but experimental studies are quite scarce. In this work, we use both numerical and experimental approaches to study pair-wise interactions between flagellated microorganisms. We use a multi-camera microscopy set-up to track the green alga Chlamydomonas reinhardtii, and characterize the physical interactions between two isolated cells.  A three-bead spring model is used to investigate the pair-wise interactions among puller type micro-organism and corroborate our experimental results. Our setup allows us to obtain three dimensional trajectories by which we can compare numerical and experimental results. These results are discussed in terms of relative velocity and relative swimming positions.