On the origin of bioconvective fluid instabilities in Tetrahymena culture systems

Abstract

Fluid instability in cultures of Tetrahymena pyriformis termed “bioconvection” [Science 133, 1766, 1961] was examined during various stages of population growth. Subsurface swarms and sedimenting droplets or vertical columns of cells were observed microscopically and macroscopically.

Analyses of their establishment, persistence and internal dynamics support the hypothesis that (1) bioconvection by such cells may be explained as a precipitation of a randomly formed subsurface region R of swarming cells that achieves a certain minimum width (0.3 cm) density contrast (2 × 10⁻⁴ g/cm³) between itself and the underlying fluid and sedimentation velocity (0.07 cm/sec). (2) viscous instability then shapes the falling R into a vertical column.