Sulfate reducing bacteria

These are the bacteria that can use sulfate to accept the electrons during anaerobic conditions. These are basically the anaerobic bacteria that reduce sulfate into hydrogen sulfide.

Examples:

Examples are purple sulfur bacteria and sulfur green bacteria.

Characteristics:

The characteristics of the sulfur-reducing bacteria are as follows:

• These bacteria are present in sediments, sea waters and area where the rich source of decay organic matter is present.
• They are present in anaerobic conditions.
• They produce a rotten egg smell by producing H₂S gas.
• They produce metal sulfide when they react with hydrogen sulfide.
• These metal sulfides are insoluble and brown to red in colour.
• These bacteria produce metal sulfides that lead to the dark colour of sludge.

Why bacteria use sulfate?
These bacteria grow in anaerobic conditions. They can’t use oxygen as electron terminal acceptor. They reduce inorganic sulfate into hydrogen sulfide. Sulfur accepts the electron from ETC. Some microbes assimilate sulfur to fulfil their sulfur requirement. They may use organic sulfur to fulfil their requirement.

SO₄➡ SO₃^-2 ➡H₂S

This is done by sulfate reductase enzymes

Classification of sulfate-reducing bacteria:

These are of following types.

• Organotrophic
• Lithotrophic
• Phototrophic
• Chemotrophic

Organotrophic:

These are the bacteria that oxidize organic compounds such as carbohydrates, organic alcohols and acids and aromatic hydrocarbons. They obtain electron acceptor from the oxidation organic compounds.

Lithotrophic:

These bacteria use inorganic compounds for the acceptance of electron. They oxidize the molecular hydrogen and use them as an electron acceptor. They live in anaerobic conditions and compete with methanogens. They can use inorganic iron as an electron acceptor.

Phototrophic:

These bacteria can prepare their own food by photosynthesis. They can use light energy and fix the CO₂ into food. They have bacterial chlorophyll that can convert light energy into glucose. They are commonly green sulfur bacteria.

Chemotrophic:

These bacteria can’t prepare their own food. They use chemical to get energy and use organic carbon for its requirement. They don’t have bacterial chlorophyll to convert light energy into glucose. They are purple sulfur bacteria.

Importance:

These bacteria are important as

• They remove hydrocarbons from the contamination soil.
• These bacteria deal with acid mine water to remove the other microbes from them.
• These bacteria are used to remove oil from contaminated water.
• They can cause corrosion of iron