Gas vacuoles are air-filled, cylindrical compartments present in prokaryotes. They help in the buoyancy.
Gas vacuoles are found in many aquatic bacteria such as blue-green algae or cyanobacteria, halophilic archaea, e.g. Halobacterium halobium, green bacteria, e.g. Pelodictyon clathratiforme, purple sulfur bacteria, etc.
Gas Vacuole Structure
Gas vacuoles are an aggregation of many gas vesicles. The shape and distribution of gas vesicles differ in various organisms. In cyanobacteria, gas vesicles are long and form parallel bundles, whereas, in purple sulfur bacteria, they are shorter and distributed irregularly.
- Gas vacuoles are protein bound structures. Each gas vesicle is surrounded by protein membrane.
- The internal part of the vesicle is hydrophobic so it does not allow entry of water.
- The diameter of gas vesicles is around 75 nm and the length ranges from 200 to 1000 nm.
Regulation of Gas Vacuole Formation
Gas vesicle synthesis is regulated by proteins and extracellular environmental factors.
- High light intensity inhibits the synthesis of gas vesicles. In Anabaena, high light intensity collapses gas vesicles due to accumulation of photosynthetic products and higher turgor pressure. High light intensity exposure at the surface can also damage the bacterial genome.
- Synthesis of gas vesicles is also regulated by oxygen level. Lack of oxygen inhibits vesicle formation in halophilic archaea.
- Accumulation of carbohydrates decrease synthesis of vesicles.
- An increase in the pH of the environment leads to increased production of vesicles in some species.
Gas Vacuole Function
Gas vacuoles help bacteria in buoyancy and enable them to float at the desired depth. They do so by inflating and deflating the vesicles. Main functions include:
- They help the photosynthetic bacteria in getting optimal light and oxygen.
- These gas vesicles show coordinated movement with light. They help bacteria come near the surface during daytime and trap the light to perform photosynthesis. At night it enables them to go deeper to extract nutrients.
- Gas vesicles help bacteria maintain salinity, prevent osmotic shock and sustain extreme environments. E.g. Halobacterium, a halophile, has gas vesicles, which help them float in salt water.
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