Anoxygenic Photosynthesis - When hydrogen sulphide is present and sufficient illumination is available purple as well as green sulphur bacteria like Chlorobium and Chromatium start primary production through anoxygenic Photosynthesis.
These bacterial species are provided with either gas vacuoles or flagella so that they can be maintained just below the metalimnion to trap any available light. Gas vacuole containing bacteria occurring in this region include Amoebobacter, Lamprocystis, Thiopedia, Thiodictyon and Ancalochloris.
