Green Sulfur Bacteria

  1. Structure
    1. Rods, spheres, or spirals
    2. May form stalks or appendages (prosthecae). These are also found in the Proteobacteria, and in the Planctomyces group.
    3. Nonmotile
      1. None are flagellate, but one is capable of gliding
    4. May have gas vesicles
    5. Do not have intracytoplasmic membrane systems
    6. Form chlorosomes, and have nonunit cell membrane
    7. One (Pelodictyon) is capable of branching, and forms a filamentous mat
  2. Photosynthesis
      Bacteriochlorophylls c, d, or e, with small amounts of chlorophyll a
    1. Reaction center P840, with Bchl a
    2. Carotenoids in the isorenieratene and chlorobactene groups
    3. Ultimate electron donor generally sulfide, with elemental sulfur accumulating outside of the cells
      1. Sulfer is further oxidized to sulfate
      2. Thiosulfate or hydrogen can sometimes be electron donor
    4. Photosystem-I like photosystem (Fe-S type)
      1. Heterodimeric reaction center
      1. Electron acceptor is FeS, with a redox potential of -0.5 V
      2. This is adequate to reduce ferredoxin, and thus can reduce NAD+ to NADH directly (unlike proteobacteria).
    5. Lack rubisco
      1. Carbon fixation by reverse TCA (Tricarboxylic acid cycle)
  3. Classification
    1. One family, the Chlorobiaceae
    2. A relatively small group of bacteria, closely related to the Bacteroides group
    3. Further divided into green and brown groups
  4. Representative Organisms
    1. Chlorobium
  5. Ecology
    1. Photolithotrophic; can grow with CO2 as sole carbon source
      1. Can also use acetate as a carbon source
    2. Strict anaerobes
    3. Obligate phototrophs

Required Reading:

Supplementary Reading:

The Prokaryotes; chapter 195

Blankenship, R., M.T. Madigan, and C. Bauer (eds.) 1996. Anoxygenic Photosynthetic Bacteria. Kluwer, Dordrecht & Boston.