bio

Gas vesicle

A hollow, rigid, sub-micrometre protein shell that lets cyanobacteria and some archaea float in a water column. The subtlety is that they are not pumped full of anything: the hydrophobic interior excludes liquid water while ambient gases diffuse in freely until pressures equalise, so the cell gains buoyancy without doing any pumping work. Regulation is destructive — once the cell accumulates enough dense carbohydrate, internal turgor exceeds the critical pressure and crushes the vesicles to sink. The mechanism cannot be scaled into an aerostat: in water it exploits a density difference of a thousand kilograms per cubic metre, while in air that figure is barely above one, and the protein shell outweighs its own lift by orders of magnitude.