Gas vacuoles

Gas vacuoles are made up of gas vesicles, which are hollow cylindrical structures. They’re found inside some microorganisms. Each gas vesicle was bound by a gas-permeable membrane. The bacterium’s buoyancy is provided by the expansion and deflation of its vesicles, which allows it to float at a chosen depth in the water. Gas vacuoles are found in microorganisms known as cyanobacteria. Cyanobacteria, often known as blue-green algae, are bacteria that live in water and produce their food using sunlight’s photosynthetic energy. The expansion and deflation of gas vesicles are synchronised with light, according to studies. Because of the buoyancy given by the gas vacuoles, bacteria may float near the top during the day to take advantage of the availability of sunlight for food production, and descend deeper at night to gather nutrients that have sunk into the water.

Structure

Gas vesicles are hollow protein tubes with conical caps on both ends that are usually lemon-shaped or cylindrical. The diameter of the vesicles varies the most. Larger vesicles can contain more air and utilise less protein, making them the most resource-efficient. However, the larger a vesicle is, the weaker it is under pressure and the less pressure is necessary before it collapses. Organisms have evolved to be the most effective in their protein use and to employ the widest maximal vesicle diameter that can resist the pressure to which they may be subjected. The diameter of gas vesicles must be regulated by genetics for natural selection to have altered them. Even though genes for gas vesicles may be identified in many haloarchaea species, only a few species generate them. From Halobacterium sp. NRC-1, the first Haloarchaeal gas vesicle gene, GvpA, was cloned.  In haloarchaea, 14 genes are involved in the formation of gas vesicles. 

GvpA, the first gas vesicle gene, was discovered in Calothrix.  The gas vesicle of a cyanobacterium is made up of at least two proteins: GvpA and GvpC. GvpA is responsible for the formation of ribs and a large portion of the major structure’s bulk (up to 90%). GvpA is very hydrophobic, maybe one of the most hydrophobic proteins yet discovered. GvpC is hydrophilic and serves to maintain the structure by inserting itself into the GvpA ribs regularly. GvpC can be washed out of the vesicle, resulting in a reduction in the strength of the vesicle. The vesicle’s wall thickness can range from 1.8 to 2.8 nm. The vesicle’s ribbed structure can be seen on both the inner and exterior surfaces, with rib spacing of 4–5 nm. Vesicles range in size from 100 to 1400 nm in length and 45 to 120 nm in diameter. Gas vesicle diameters within a species are very consistent, with a standard variation of 4%.

Growth

Gas vesicles appear to start as little biconical structures (two cones with flat bottoms linked together) that extend to a particular diameter before growing and expanding their length. It’s unclear what governs the diameter; it might be a molecule that interacts with GvpA, or GvpA’s shape could alter.

Uses of Gas vacuoles

1. Role in vaccine development

The protein expressed by the gas vesicle gene gvpC has several properties that make it suitable for use as an antigen carrier and adjuvant: it is stable, resistant to biological degradation, tolerate relatively high temperatures (up to 50 °C), and is non-pathogenic to humans.  Several antigens from several human infections have been recombined with the gvpC gene to construct long-lasting subunit vaccinations. The gvpC gene of Halobacteria is connected to several genomic regions encoding for numerous Chlamydia trachomatis pathogen proteins, including MOMP, OmcB, and PompD. In vitro cell evaluations reveal the expression of Chlamydia genes on cell surfaces using imaging methods, as well as immunologic responses such as TLR activity and the generation of pro-inflammatory cytokines. The gas vesicle gene might be used as a delivery mechanism for a possible Chlamydia vaccination. The necessity to reduce GvpC protein degradation while inserting as much of the vaccination target gene into the gvpC gene section is one of the method’s limitations. 

2. Role as contrast agents and reporter genes

Gas vesicles contain several physical characteristics that allow them to be seen in a variety of medical imaging modalities.  For decades, the capacity of gas vesicles to scatter light has been employed to estimate concentration and measure collapse pressure. Gas vesicles’ optical contrast allows them to be used as contrast agents in optical coherence tomography, which has uses in ophthalmology.   Gas vesicles have a lot of acoustic contrast because of the differential in acoustic impedance between the gas in their cores and the surrounding fluid.   Furthermore, the capacity of some gas vesicle shells to buckle produces harmonic ultrasound echoes, which increases the contrast to tissue ratio. Finally, because of the difference in magnetic susceptibility of air and water, gas vesicles can be utilised as contrast agents for magnetic resonance imaging (MRI). The ability to use pressure waves to non-invasively collapse gas vesicles gives a way for deleting their signal and increasing the contrast. Background signals may be removed by subtracting the pictures before and after the acoustic collapse, which improves the identification of gas vesicles.

Conclusion

Gas vesicles, also known as gas vacuoles, are nano compartments that aid buoyancy in some bacterial species. Gas vesicles are exclusively made up of protein, with no lipids or carbs found. Gas vesicles are found largely in aquatic animals, where they are used to adjust the buoyancy of the cell and change its position in the water column so that it can be better positioned for photosynthesis or travel to areas with more or less oxygen. Organisms that can float to the air-liquid interface outcompete other aerobes that can’t climb through the water column by depleting oxygen in the top layer. Gas vesicles are hollow protein tubes with conical caps on both ends that are usually lemon-shaped or cylindrical. The diameter of the vesicles varies the most. Larger vesicles can contain more air and utilise less protein, making them the most resource-efficient. However, the larger a vesicle is, the weaker it is under pressure and the less pressure is necessary before it collapses.