Green Non-Sulfur Bacteria

Green Non-Sulfur Bacteria

·       Example – Chloroflexus aurantiacus, Chloronema giganteum, Oscillochloris trichoides and Herpetosiphon aurantiacus.

·       Number of Species – Around 30 – 35 species.

·       Habitat – Hot springs, alkaline springs, marine sediments, microbial mats, geothermal areas; thrive in hot, low-oxygen, illuminated environments.

·       Mode of Nutrition

ü  Photoheterotrophy (Primary Mode): They preferentially use light for energy but require organic compounds (e.g., sugars, amino acids, organic acids) as carbon sources.

ü  Photoautotrophy (Alternative Mode): Some, like Chloroflexus, can fix CO₂, but they use a unique pathway called the 3-Hydroxypropionate pathway, which is different from the Calvin cycle (used by plants and purple bacteria) and the rTCA cycle (used by green sulfur bacteria).

ü  Chemoheterotrophy: In the dark, they can grow aerobically by respiring organic compounds.

·       Mode of Reproduction – Binary fission or Fragmentation.

·       Mode of Respiration – Many members are facultative aerobes, aerobically respire organic compounds in darkness, but switch to anoxygenic phototrophy under suitable light conditions.

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

·       Pigments

ü  Bacteriochlorophyll c, d, or e: Located in unique structures called chlorosomes, similar to Green Sulfur Bacteria. (Roseiflexus lacks chlorosomes and uses Bchl a).

ü  Bacteriochlorophyll a: Found in the reaction centers embedded in the cytoplasmic membrane.

ü  Carotenoids (e.g., γ-carotene, Beta-carotene): These often give them a distinctive orange color.

·       Electron Donor – Organic compounds, H₂, H₂S (low levels), and sometimes reduced sulfur compounds.

·       By-products – Produce organic acids or sulfur globules depending on species.

·       Photosystem – Photosystem II–type is present; Cyclic photophosphorylation.

·       Ecological role

ü  Important primary producers in hot springs and microbial mats.

ü  Contribute to carbon fixation in extreme environments.

ü  Participate in decomposition of organic matter under anaerobic conditions.

ü  Early evolutionary link between cyanobacteria and green sulfur bacteria.