Question:

Conversion of organic matter to biogas proceeds in four stages: hydrolysis, acidogenesis, acetogenesis, and methanogenesis. Which one of the following microorganisms plays a key role in the methanogenesis conversion stage?

1. Yeast

2. Phototrophic bacteria

3. Archaea

4. Aerobic bacteria

Correct Answer:

3. Archaea

Detailed Explanation:

Biogas production is a complex process that involves the conversion of organic matter, such as plant and animal waste, into methane and other gases. This process occurs in several stages, each facilitated by different types of microorganisms. Here’s an overview of each stage and the microorganisms involved:

1. Hydrolysis:

• During this initial stage, complex organic matter (such as fats, proteins, and carbohydrates) is broken down into simpler compounds (like sugars, amino acids, and fatty acids) by hydrolytic bacteria.

2. Acidogenesis:

• In this stage, the products from hydrolysis are further broken down into short-chain fatty acids, alcohols, hydrogen, and carbon dioxide by acidogenic bacteria.

3. Acetogenesis:

• Acetogenic bacteria then convert the products from acidogenesis into acetic acid, hydrogen, and carbon dioxide, which are crucial substrates for the next stage.

4. Methanogenesis:

• This final stage is where methanogenic archaea play a critical role. These microorganisms convert the byproducts from acetogenesis (mainly acetic acid and hydrogen) into methane (CH₄) and carbon dioxide (CO₂).

• Archaea are a unique group of microorganisms distinct from bacteria and are the only organisms capable of producing methane through the process of methanogenesis. The key genera involved in methanogenesis include Methanobacterium, Methanosaeta, and Methanococcus.

Why Archaea play a key role in methanogenesis:

• Archaea are the only microorganisms that can perform methanogenesis, a unique process where methane is produced as a metabolic end product. Other microorganisms, such as bacteria or yeast, are not involved in this final step.

• Methanogenesis is crucial for the production of biogas, and methanogenic archaea thrive in anaerobic conditions, which are typical in biogas reactors.

Conclusion:

The correct answer is Archaea, as they are the key microorganisms involved in the methanogenesis stage of biogas production. They are responsible for converting organic acids and hydrogen into methane, a major component of biogas.