Purple Non-Sulfur Bacteria

 Purple Non-Sulfur Bacteria

·       Example – Rhodospirillum rubrum, Rhodobacter sphaeroides, Rhodopseudomonas palustris and Rhodomicrobium vannielii

·       Number of Species – There are over 100 described species across multiple genera, and new species are still being discovered and characterized thanks to modern genetic techniques.

·       Habitat – Anoxic environments such as freshwater, marine sediments, paddy soils, and wastewater, and can persist in both aquatic and terrestrial settings even when environmental conditions fluctuate.

·       Mode of Nutrition

ü  Photoheterotrophs, using light for energy and organic compounds as carbon sources.

ü  Photoautotrophy (using CO₂ as a carbon source).

ü  Chemoheterotrophy (respiring organic matter in the dark).

ü  Mixotrophy depending on light and oxygen availability.

·       Mode of Reproduction – Asexual reproduction by Binary fission; Rhodomicrobium reproduces by Budding.

·       Mode of Respiration – Facultative anaerobes (Anaerobic in light; Aerobic in dark).

·       Type of Photosynthesis

ü  Anoxygenic photosynthesis - Do not evolve oxygen, using light to generate energy in the absence of water splitting.

ü  The photosynthetic process is cyclic, utilizing a single Photosystem (typically referred to as Photosystem I-like, with a reaction center P870 or P960).

·       Pigments

ü  Bacteriochlorophyll a or b: The primary photosynthetic pigment, absorbing light in the near-infrared range (longer wavelengths than plant chlorophyll).

ü  Carotenoids (e.g., Spirilloxanthin, Lycopene): These accessory pigments give them their characteristic brown, red, or purple color. They absorb light in the Blue-green range and also serve a photoprotective role.

·       Electron Donor – Organic acids (acetate, lactate, succinate), Alcohols, Hydrogen, Hydrogen sulphide at very low levels.

·       By-products – CO₂, various Organic acids, and, under nitrogen-fixing conditions, Ammonia.

·       Photosystem – Photosystem I (anoxygenic) & Cyclic photophosphorylation.

·       Ecological role

ü  Recycle organic matter in anaerobic zones.

ü  Nitrogen fixation (many species fix atmospheric N₂).

ü  Bioremediation of wastewater and heavy metals.

ü  Used in hydrogen biofuel production.

ü  Improve soil fertility in rice fields and wetlands.