Life mode of Thiomargarita namibiensis: Most of the time the cells are buried in the sediment with very high sulfide concentration and no access to nitrate. Under these conditions they can take up and store sulfide as elemental sulfur which they may oxidize further to sulfate for gaining energy. For both oxidation steps internally stored nitrate is reduced to ammonia. Occasionally the very loose sediments may get resuspended and the cells gain access to nitrate which they take up and concentrate in the vacuole. When the sediment is suspended in the oxic water column cells, Thiomargarita cells may gain energy by oxidizing either internal sulfur or sulfide if present.