A range of bacteria and archaea produce intracellular gas-filled proteinaceous 
structures that function as flotation devices in order to maintain a suitable 
depth in the aqueous environment. The wall of these gas vesicles is freely 
permeable to gas molecules and is composed of a small hydrophobic protein, GvpA, 
which forms a single-layer wall. In addition, several minor structural, 
accessory or regulatory proteins are required for gas vesicle formation. In 
different organisms, 8-14 genes encoding gas vesicle proteins have been 
identified, and their expression has been shown to be regulated by environmental 
factors. In this Review, I describe the basic properties of gas vesicles, the 
genes that encode them and how their production is regulated. I also discuss the 
function of these vesicles and the initial attempts to exploit them for 
biotechnological purposes.