Flexibacter (fleck-see-back-ter) - a bacterium isolated from a marine sediment. Benthic ecosystems in marine and many other sediments is one which has a spectacular range of chemical conditions - from an oxic habitat at the surface to an anoxic, sulphide and acidic habitat in deeper regions. The oxygen rich layer penetrates deeper into sediments during the day or when sediments are exposed to the air (photosynthesis and access to the atmosphere provide a supply of oxygen), and at night or when the tide comes up the oxygen rich layer recedes. Most organisms seem to occur only in a narrow band within the habitats, and so must be able to move with the changing chemistry of the habitat changes. Many bacteria - such as the ones illustrated here - are filamentous and flexible and can migrate through the sediments. Phase contrast.