Ionic propulsion in a non-motile dinoflagellate.

For hundreds of years, a subset of phytoplankton cells deemed 'bladder type' have been observed to occupy niches in nutrient poor, low light ocean habitats. Defining features of these organisms include their large volume, as well as their ability to transit vertical distances of 10's of meters with no cilia or flagella. Therefore, an obvious question exists; how do cells lacking mechanical propulsion orient themselves in the water column? Without mechanical means, how do they change their position? Fundamentally, since cytoplasmic density of cells is often 5-10% heavier than water, these eukaryotic cells evolved in the ocean to integrate environmental signals such as light, pressure, salinity, and nutrients to control their buoyancy in the water column with regulated ion flux and concomitant volume changes. Using high-resolution vertical tracking microscopy along with molecular perturbations we describe a coordinated order of magnitude volume increase that takes place in under 15 minutes to rapidly decrease sedimentation speed after cell division. We use electron and light sheet microscopy along with modeling to describe how the cellular design principles behind Pyrocystis's cellular morphology enable it to cope with rapid inflation while conserving biochemical function.