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. When nitrate concentrations in the environment are low, the bacterium uses the contents of its vacuole for respiration. Thus, the presence of a central vacuole in its cells enables a prolonged survival in sulfidic sediments. The non-motility of "Thiomargarita" cells is compensated by its large cellular size.