Difference between Green and Purple Sulfur Bacteria

Green Sulfur Bacteria

It is a group of photoautotrophic bacteria that can perform anoxygenic photosynthesis. Most of them are nonmotile and obligate anaerobes. They have bacteriochlorophyll pigments c, d, a or e. Also, they use sulphide as their ultimate electron donor for photosynthesis. Thus, they can thrive well in sulfur-rich environments with low light intensities.

Most of these bacteria can reduce nitrogen to ammonia. This ammonia is later used to synthesise amino acids.

Purple Sulfur Bacteria

It is a group of photosynthetic proteobacteria. They can be microaerophilic or anaerobic and are usually often found in hot springs. They have bacteriochlorophyll pigment a or b. These pigments are located on chromatophores and plasma membranes. They use sulfide or thiosulfate as their electron donor during photosynthetic pathways. The sulfur deposition occurs inside the bacterial cell.

The purple sulfur bacteria can be used to reduce the concentration of harmful compounds like methane and hydrogen sulfide.

Also Read: Difference between Bacterial Photosynthesis and Plant Photosynthesis

Difference between Green and Purple Sulfur Bacteria

Green Sulfur Bacteria

Purple Sulfur Bacteria


Phylum Chlorobiota and order Chlorobiales.

Phylum Proteobacteria and order Chromatiales.


Bacteriochlorophyll pigments c, d, a or e

Bacteriochlorophylls a or b

Location of pigments

Chlorosome and Plasma membrane.

Chromatophore and Plasma membrane.


Obligate anaerobic.

Microaerophilic or anaerobic.

Sulfur deposition

Outside the cell.

Inside the cell.

Colour of bacterial colonies

Green, yellowish-green and orangish-green.

Purple, reddish-purple and reddish-brown.


Chlorobium limicola

Spiribacter roseus

Explore: Difference between Photosynthesis and Chemosynthesis

Frequently Asked Questions on Difference between Green and Purple Sulfur Bacteria

What are bacteriochlorophylls?

They are photosynthetic pigments similar to chlorophylls. It is seen in various phototrophic bacteria like Chloroflexi, Purple and Green sulfur bacteria. Usually, the organisms with bacteriochlorophylls undergo photosynthesis without releasing oxygen as a byproduct.

What is anoxygenic photosynthesis?

It is a type of photosynthesis that uses hydrogen sulfide as a reductant (instead of water), and releases sulfur as a byproduct (instead of oxygen). It is common in heliobacteria, acidobacteria, green sulfur bacteria, purple bacteria, green and red filamentous phototrophs, etc.

What are cyanobacteria?

Blue-green algae or cyanobacteria is a gram-negative bacteria that can perform photosynthesis. They have photosynthetic pigments such as phycobilins, carotenoids and various other forms of chlorophyll. Most cyanobacteria use water as an electron donor, while some might also use hydrogen sulfide.

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