What is the Difference Between Green and Purple Sulfur Bacteria

The key difference between green and purple sulfur bacteria is that green sulfur bacteria are a group of sulphur bacteria that appear in yellow-green, green-orange or brown colour while purple sulphur bacteria are a group of proteobacteria that appear in a purple or reddish-brown colour.

Cyanobacteria are a group of bacteria that can do photosynthesis. They capture light in order to produce their own food. As a by-product, they release oxygen to the environment. Hence, this type of photosynthesis is known as oxygenic photosynthesis. There are several other groups of bacteria that carry out photosynthesis, but they do not produce oxygen. This type of photosynthesis is known as anoxygenic photosynthesis. Green sulphur bacteria and purple sulphur bacteria are two such groups. They absorb light via bacteriochlorophylls and produce ATP.  But they do not use water as an electron donor. Instead, they use sulphides and produce granules of elemental sulphur. Hence, they do not release oxygen.

CONTENTS

1. Overview and Key Difference
2. What is Green Sulfur Bacteria
3. What is Purple Sulfur Bacteria
4. Similarities – Green and Purple Sulfur Bacteria
5. Green vs Purple Sulfur Bacteria in Tabular Form
6. Summary –Green vs Purple Sulfur Bacteria

What are Green Sulfur Bacteria?

Green sulphur bacteria are a group of photoautotrophic bacteria. They are obligate anaerobes that are closely related to bacteroidetes. Furthermore, green sulphur bacteria can adapt to a narrow range of energy-limited conditions. The ecology of green sulphur bacteria is similar to cyanobacteria. These bacteria are non-motile. They are mostly spheres, rods, and spiral forms. Green sulphur bacteria belong to the family Chlorobiaceae and Chlorobium, Chlorobaculum, Prosthecochloris, and Chloroherpeton are several genera of green sulphur bacteria.

Green sulfur bacteria possess bacteriochlorophyll (BChl) c, d, or e, in addition to BChl a and chlorophyll a. They carry out anoxygenic photosynthesis. Therefore, they convert light energy into ATP without the production of oxygen. Moreover, the light-dependent reaction is noncyclic, so they generate NADPH. Photosynthetic reaction centre or RC complex of green sulphur bacteria shares structural and functional similarities with the photosystem 1 complex of plants and cyanobacteria.

What are Purple Sulfur Bacteria?

Purple sulphur bacteria are another group of bacteria that are capable of doing anoxygenic photosynthesis. They are a group of proteobacteria that are gram-negative. These bacteria are anaerobic or microaerophilic. They often live in hot springs or stagnant water. They cannot live in oxygenated environments. In order to control purple sulphur bacteria in water bodies, the dissolved oxygen concentration should be increased. These bacteria use hydrogen sulphide as the reducing agent instead of water. Hence, they do not produce oxygen. They produce granules of elemental sulfur.

Since purple sulphur bacteria depend on sulphides for photosynthesis, high sulfide concentrations and high ammonia concentrations can promote the growth of green sulfur bacteria. There are two families of purple sulphur bacteria. They are Chromatiaceae and Ectothiorhodospiraceae.

What are the Similarities Between Green and Purple Sulfur Bacteria?

• Both green sulphur bacteria and purple sulphur bacteria are able to carry out anoxygenic photosynthesis.
• They do not produce oxygen during photosynthesis.
• Both can capture light and produce ATP.
• They have photosynthetic pigments called bacteriochlorophylls.
• They use hydrogen sulphide as the reducing agent.
• Hence, they are integral parts of the Sulfur cycle.
• Both are Gram-negative bacteria.

What is the Difference Between Green and Purple Sulfur Bacteria?

Green sulphur bacteria and purple sulphur bacteria are two groups of sulphur bacteria that undergo anoxygenic photosynthesis. Green sulphur bacteria appear in yellowish-green, greenish-orange or brown, while purple sulphur bacteria appear in purple or reddish-brown. So, this is the key difference between green and purple sulphur bacteria.

The below infographic lists the differences between green and purple sulphur bacteria in tabular form for side by side comparison.

Summary – Green vs Purple Sulfur Bacteria

Green sulphur bacteria and purple sulphur bacteria are two groups of bacteria that undergo anoxygenic photosynthesis. Therefore, they are photoautotrophic bacteria. Green sulphur bacteria appear in yellowish-green or green-orange, or brown in colour. They are closely related to bacteriodetes. Purple sulphur bacteria appear in purple or brown in colour, and they belong to proteobacteria. Furthermore, green sulphur bacteria absorb larger wavelength light than purple sulphur bacteria. Thus, this summarizes the difference between green and purple sulphur bacteria.

Reference:

1. “Nonproteobacteria Gram-Negative Bacteria.” Lumen.
2. “Green Sulfur Bacteria.” Wikipedia, Wikimedia Foundation, 1 Oct. 2021.

Image Courtesy:

1. “Green d winogradsky” By kOchstudiO – Mikrobiologie Praktikum Universität Kassel März 2007 (Public Domain) via Commons Wikimedia
2. “Purple and Green Sulfur Bacteria and Their Biomarkers” By Alatleephillips – Own work (CC BY-SA 4.0) via Commons Wikimedia