The formation of gas vesicles has been investigated in bacteria and haloarchaea for more than 50 years. These air-filled nanostructures allow cells to stay at a certain height optimal for growth in their watery environment. Several gvp genes are involved and have been studied in Halobacterium salinarum, cyanobacteria, Bacillus megaterium, and Serratia sp. ATCC39006 in more detail. GvpA and GvpC form the gas vesicle shell, and additional Gvp are required as minor structural proteins, chaperones, an ATP-hydrolyzing enzyme, or as gene regulators. We analyzed the Gvp proteins of Hbt. salinarum with respect to their protein-protein interactions, and developed a model for the formation of these nanostructures. Gas vesicles are also used in biomedical research. Since they scatter waves and produce ultrasound contrast, they could serve as novel contrast agent for ultrasound or magnetic resonance imaging. Additionally, gas vesicles were engineered as acoustic biosensors to determine enzyme activities in cells. These applications are based on modifications of the surface protein GvpC that alter the mechanical properties of the gas vesicles. In addition, gas vesicles have been decorated with GvpC proteins fused to peptides of bacterial or viral pathogens and are used as tools for vaccine development.
Keywords: Halobacterium salinarum; acoustic biosensors; gas vesicles; protein nanostructures; vaccine development.