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Gas-filled vesicles are protein-shelled, gas-filled compartments found in some aquatic microorganisms that regulate buoyancy. They are intracellular organelles observed in a subset of cyanobacteria, certain bacteria, and some archaea, enabling cells to adjust their position in the water column in response to light, nutrients, and gas exchange needs.

The vesicles have a rigid, gas-impermeable shell primarily built from the protein GvpA, often reinforced by GvpC and other associated proteins. The resulting shell forms a hollow lumen that remains filled with air or other gases. The shell’s properties allow diffusion of gases while restricting liquid water, and the vesicles are mechanically fragile and collapse under increasing hydrostatic pressure. The ability to rapidly synthesize and degrade these structures enables dynamic buoyancy control.

Buoyancy is the principal ecological function: by adjusting vesicle number and gas content, cells can move toward surface waters for photosynthesis or descend to pursue nutrients or avoid excess light. The expression of gas vesicle gene clusters, typically containing gvpA, gvpC, and several accessory genes, is regulated by environmental cues such as light intensity, nutrient availability, and oxygen levels. Vesicle assembly occurs in the cytoplasm and is coordinated to produce functional gas-filled compartments.

Distribution varies by lineage. Gas-filled vesicles have been described in cyanobacteria and in certain proteobacteria, as well as in haloarchaea, reflecting convergent evolution of buoyancy strategies in aquatic ecosystems.

In biotechnology, gas vesicles and their protein shells have been explored as nanoscale acoustic contrast agents for ultrasound and as platforms for surface display of peptides, highlighting ongoing research into their biomedical applications.