Microalgae Scatter off Solid Surfaces by Hydrodynamic and Contact Forces

Abstract

Interactions between microorganisms and solid boundaries play an important role in biological processes, like egg fertilisation, biofilm formation and soil colonisation, where microswimmers move within a structured environment. Despite recent efforts to understand their origin, it is not clear whether these interactions can be understood as fundamentally of hydrodynamic origin or hinging on the swimmer's direct contact with the obstacle. Using a combination of experiments and simulations, here we study in detail the interaction of the biflagellate green alga Chlamydomonas reinhardtii, widely used as a model puller microorganism, with convex obstacles, a geometry ideally suited to highlight the different roles of steric and hydrodynamic effects. Our results reveal that both kinds of forces are crucial for the correct description of the interaction of this class of flagellated microorganisms with boundaries.

Guiding microscale swimmers using teardrop-shaped posts

“…Higher concentrations of microswimmers near surfaces have been attributed to a combination of hydrodynamic and steric interactions [11,12,13,14]. When E. coli bacteria or Chlamydomonas algae encounter a surface, they are deflected at a small scattering angle that is independent of the angle of incidence [15,16].…”

Helicobacter pyloriCouples Motility and Diffusion to Actively Create a Heterogeneous Complex Medium in Gastric Mucus

“…The effect of non-Newtonian environments and geometrical confinement [25][26][27][28][29][30][31][32][33][34] have both been the subject of much research, including situations combining the two [35][36][37]. Usually, medium rheology and geometrical configuration are considered a background environment that microorganisms do not change during swimming [38].…”

Tailored environments to study motile cells and pathogens

“…C. reinhardtii has been studied using different types of pillar arrays including “inverse pillar,” that is, cylindrical wells (Contino, Lushi, Tuval, Kantsler, & Polin, ; Ostapenko et al, ). In the absence of confinement, C. reinhardtii migration is diffuse, whereas within the confined cylindrical wells, movement is predominantly along the curved wall surfaces (Contino et al, ; Ostapenko et al, ). This revealed that increased movement along curved surfaces in confinement is not restricted to microorganisms driven by posterior appendages but is also found in microorganisms with anterior flagella.…”

“…For example, the microalga Chlamydomonas reinhardtii is a soil-dwelling organism that pulls itself with two flagella. C. reinhardtii has been studied using different types of pillar arrays including "inverse pillar," that is, cylindrical wells (Contino, Lushi, Tuval, Kantsler, & Polin, 2015;Ostapenko et al, 2017). In the absence of confinement, C. reinhardtii migration is diffuse, whereas within the confined cylindrical wells, movement is predominantly along the curved wall surfaces (Contino et al, 2015;Ostapenko et al, 2017).…”