Green Sulfur Bacteria

 Green Sulfur Bacteria

·       Example – Chlorobium limicola, Chlorobaculum tepidum, Prosthecochloris aestuarii and Pelodictyon luteolum.

·       Number of Species – Over 90 species, found mainly in the family Chlorobiaceae.

·       Habitat

ü  Anaerobic zones of lakes and ponds, sulfur-rich environments, stagnant waters, sulfur springs, marine sediments.

ü  Live in deep, low-light zones where H₂S is abundant.

·       Mode of Nutrition – Obligate photoautotrophs (use light as energy and CO₂ as carbon source).

·       Mode of Reproduction – Binary fission (Asexual mode)

·       Mode of Respiration – Obligate anaerobes (cannot survive in presence of oxygen).

·       Type of Photosynthesis – Anoxygenic photosynthesis (do not use water as an electron donor and do not produce oxygen).

·       Pigments

ü  Bacteriochlorophylls c, d, or e (located in chlorosomes)

ü  Accessory Pigments: carotenoids (give green, brown, orange coloration)

·       Electron Donor

ü  Primary Donor: Reduced sulfur compounds, most commonly hydrogen sulfide (H₂S). They can also use elemental sulfur (S⁰) and thiosulfate (S₂O₃²⁻).

ü  Other Donors: Some species can use hydrogen (H₂) or ferrous iron (Fe²⁺) as an electron donor.

·       By-products – Elemental Sulfur.

·       Photosystem – Uses Photosystem I – type only (Cyclic photophosphorylation); highly efficient due to chlorosomes which capture weak light.

·       Ecological role

ü  Key organisms in sulfur cycle (oxidize H₂S → S⁰ → SO₄²⁻).

ü  Primary producers in deep anoxic water layers.

ü  Support food chain in sulfur-rich lakes and hot springs.

ü  Indicators of polluted, oxygen-poor environments.

ü  Used in bioremediation of sulfur-contaminated habitats.