What is the Difference Between Hydrogenotrophic and Acetoclastic Methanogenesis

The main difference between hydrogenotrophic and acetoclastic methanogenesis is that hydrogenotrophic methanogenesis uses H₂ and CO₂ to carry out methanogenesis whereas acetoclastic methanogenesis uses acetate as the electron acceptor for methanogenesis.

Hydrogenotrophic and acetoclastic methanogenesis are two types of methanogenesis that occur in most extreme anaerobic conditions. The third type of methanogenesis is methylotrophic methanogens that use methanol or methylamines as the electron acceptor.

Key Areas Covered

1. What is Hydrogenotrophic Methanogenesis
     – Definition, Features, Importance
2. What is Acetoclastic Methanogenesis
     – Definition, Features, Importance
3. Similarities Between Hydrogenotrophic and Acetoclastic Methanogenesis
     – Outline of Common Features
4. Difference Between Hydrogenotrophic and Acetoclastic Methanogenesis
     – Comparison of Key Differences

Key Terms

Acetoclastic Methanogenesis, Hydrogenotrophic Methanogenesis

What is Hydrogenotrophic Methanogenesis

Hydrogenotrophic methanogenesis is a chemoautotrophic process that uses H₂ as the main energy source and the electron source and CO₂ as the source of cellular carbon and an electron sink. The ratio between H₂ and CO₂ is 4:1 in the reaction. It also requires hydrogen gas in nM concentrations while carbon dioxide in mM concentrations. However, the lack of the electron donor, H_2, is the major substrate limitation in the reaction. Here, 45% of hydrogenotrophic methanogens use formate as a substitution for H₂ gas. Some hydrogenotrophic methanogens require a separate organic carbon source for their growth.

Figure 1: Methanogenesis

Furthermore, hydrogenotropy is the most common form of methanogenesis. The other names of hydrogenotrophic methanogenesis include CO₂/H₂ reduction, hydrogenotrophy, or H₂ dependent methanogenesis. Most importantly, it occurs in freshwater systems such as bogs.

What is Acetoclastic Methanogenesis

Acetoclastic methanogenesis is another chemoautotrophic type of process that uses acetate as the electron acceptor. The other names of acetoclastic methanogenesis include acetate fermentation or acetotrophy. Only 10% of methanogenesis is acetoclastic. Only two genera of methanogens undergo acetoclastic methanogenesis. They include Methanosarcina and Methanosaeta (Methanothrix). Methanosarcina has a high potential growth rate, and it uses a wide variety of substrates. But its affinity to acetate is low. In comparison, Methanosaeta is specialized to use acetate and has a high affinity for the substrate. However, the potential growth rate of Methanosaeta is low.

Figure 2: Acetoclastic methanogenesis

Moreover, the substrate acetate undergoes simultaneous oxidation and reduction processes. While acetate is oxidized, it also undergoes reduction, resulting in the production of CH4 (methane). There, the methyl group of acetate is the electron donor, while the electron acceptor is the carboxyl group. In the meanwhile, acetotrophy is the most dominant methanogenesis pathway in the ecosystem, although it has a limited taxonomical distribution. It occurs in freshwater ecosystems such as fens.

Similarities Between Hydrogenotrophic and Acetoclastic Methanogenesis

• Hydrogenotrophic and acetoclastic methanogenesis are two types of methanogenesis processes that occur in most extreme anaerobic conditions.
• They are methanogens producing methane (CH₄), a potent greenhouse gas.
• They are the most common pathways in freshwater systems.

Difference Between Hydrogenotrophic and Acetoclastic Methanogenesis

Definition

Hydrogenotrophic methanogenesis refers to a chemoautotrophic process in which H₂ is the source of both energy and electrons, and CO₂ is often both an electron sink and the source of cellular carbon, while acetoclastic methanogenesis refers to the split acetate to methane and CO₂, where the methyl-group yields methane and the carboxyl-group CO₂.

Importance

Hydrogenotrophic methanogenesis uses H₂ and CO₂ to carry out methanogenesis, while acetoclastic methanogenesis uses acetate as the electron acceptor.

Occurrence

While hydrogenotrophic methanogenesis occurs in bogs, acetoclastic methanogenesis occurs in fens.

Taxonomical Distribution

Hydrogenotrophic methanogenesis is the common type of methanogenesis, while only 10% of methanogenesis is acetoclastic methanogenesis.

Conclusion

In brief, hydrogenotrophic and acetoclastic methanogenesis are two types of methanogenesis that occur in freshwater systems. Hydrogenotrophic methanogenesis occurs in the bogs. It also uses H₂ and CO₂ in methanogenesis. In addition, it is the most common type of methanogenesis. In comparison, acetoclastic methanogenesis occurs in fens. However, it uses acetate as the electron acceptor. But only 10% of methanogenesis is acetoclastic. Therefore, the main difference between hydrogenotrophic and acetoclastic methanogenesis is the type of methanogenesis.

References:

1. “Methanogenesis.” ScienceDirect Topics.
2. “Hydrogenotrophic methanogens.” ScienceDirect Topics. 

Image Courtesy:

1. “Methanogenesis cycle” By Smokefoot – Own work (CC-BY SA 4.0) via Commons Wikimedia
2. “Methanogenesis acetate.” By Yikrazuul – Own Work (CC-BY SA 3.0) via Commons Wikimedia