Gas vacuoles are found in which of the following organisms?

Gas vacuoles are found in blue-green algae, purple, and green photosynthetic bacteria. 

They are gas-filled vesicles that provide buoyancy to the cells, allowing them to regulate their position in the water column. By adjusting the amount of gas in the vacuoles, cyanobacteria can control their vertical movement, optimizing their exposure to light and nutrients.