  Microorganisms, such as bacteria and microalgae, often live in habitats
consisting of a liquid phase and a plethora of interfaces. The precise ways in
which these motile microbes behave in their confined environment remain
unclear. Using experiments, Brownian dynamics simulations, and analytical
theory, we study the motility of a single Chlamydomonas microalga in an
isolated microhabitat with controlled geometric properties. We demonstrate how
the geometry of the habitat controls the cell's navigation in confinement. The
probability of finding the cell swimming near the boundary scales linearly with
the wall curvature, as seen for both circular and elliptical chambers. The
theory, utilizing an asymmetric dumbbell model of the cell and steric wall
interactions, captures this curvature-guided navigation quantitatively with no
free parameters.
