 This is deposited as granules in its periplasm and is highly refractile and opalescent, making the organism look like a pearl.While the sulfide is available in the surrounding sediment, produced by other bacteria from dead microalgae that sank down to the sea bottom, the nitrate comes from the above seawater.Since the bacterium is sessile, and the concentration of available nitrate fluctuates considerably over time, it stores nitrate at high concentration (up to 0.8 molar) in a large vacuole like an inflated balloon, which is responsible for about 80% of its size.