Original paper

Variation in sinking velocity and cell size of Microcystis sp.

Walsby, Anthony E.; Lihou, Patricia; Roper, Juliet

Abstract

Measurements were made of the sinking velocity of Microcystis cells sedimenting on columns stabilised by density gradients: better results were obtained with gradients prepared with colloidal Percoll than with sucrose used previously. The variation in sinking velocity was partly explained by the variation in cell size. Measurement of cell dimensions of the unicellular cyanobacterium at five different geometrically distinguished stages of the cell cycle (spherical, ellipsoidal, cylindrical with rounded ends, overlapping spheres and double spheres) revealed a four-fold variation in cell volume at low irradiance and a ninefold variation over different irradiances. The mean cell volume of Microcystis sp. doubled when the cyanobacterium was grown at a high irradiance; the size increase occurred at all stages of the cell cycle. Cells exposed to high irradiance showed a rise in cell turgor pressure that indicated a small increase in cell volume by osmosis, but this accounted for only a small proportion of the total increase in cell volume.

Keywords

microcystiscyanobacteriacell sizesinking velocitygas vesicles