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Who is the hero of ammonia oxidation? Learn more about the amazing world of ammonia-oxidizing bacteria!
In nature, the nitrogen cycle is critical to the health of ecosystems. Among them, ammonia-oxidizing bacteria play a very special and important role. These tiny organisms can convert ammonia into nitrates and provide essential nutrients to the soil. This article will explore the key position of ammonia-oxidizing bacteria (AOB) and their sister group ammonia-oxidizing archaea (AOA) in the nitrogen cycle and how they shape this delicate but important ecological process.
The first step in the nitrogen cycle: oxidation of ammonia
The process of ammonia oxidation begins with the oxidation of ammonia (NH3) or ammonium radical (NH4+) to form nitrite (NO 2-). This process is often called ammonia oxidation, and the success of this stage is the basis of the nitrogen cycle.
These tiny organisms convert ammonia into nitrates, providing essential nutrients to the soil.
Ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) are the main organisms that perform this process, showing their diversity and adaptability in different environments. AOB usually belongs to Gram-negative bacteria and can survive widely in soil, water systems, sewage treatment plants and other places. For example, genera such as Nitrosomonas and Nitrococcus are frequently studied ammonia-oxidizing bacteria and can be found in many environments.
Ammonia-oxidizing bacteria (AOB)
Ammonia-oxidizing bacteria are known for their ability to convert ammonia into hydroxylamine. One of the key enzymes, ammonia monooxygenases (AMOs), is essential for the oxidation of ammonia to hydroxylamine. This process is quite sensitive to environmental conditions (such as pH, temperature and oxygen supply), so the distribution of ammonia-oxidizing bacteria is closely related to their environment.
Ammonia-oxidizing archaea (AOA)
Although before 2005, scientists believed that only ammonia-oxidizing bacteria were capable of oxidizing ammonia, the presence of ammonia-oxidizing archaea in sprays changed this view. Compared to AOB, AOA generally dominate soil and marine environments, making them important players in ammonia oxidation. In addition, Crenarchaeol, a compound unique to archaea, has been proposed as a biomarker for AOA, showing its correlation with ammonia oxidation.
Nitrous acid oxidation process
In the second step of the nitrogen cycle, nitrite is further oxidized to nitrate, a process commonly known as nitrite oxidation. This step is usually responsible for nitrite-oxidizing bacteria, which are found in soil, freshwater and marine ecosystems and provide the necessary support for the completion of the nitrogen cycle.
New discovery of complete ammonia oxidation
In 2015, scientists discovered that certain bacteria such as Nitrospira inopinata can oxidize ammonia to nitric acid in a single step, a discovery that revolutionized our understanding of the nitrogen cycle. In this process, the activities of many microorganisms not only support the biogeochemical cycle of nitrogen, but also provide plants with the necessary nitrates. The existence of this process undoubtedly makes us rethink the main role of microorganisms in ecosystems.
Historical background of the nitrogen cycle
Knowledge of the nitrogen cycle dates back to the 19th century, when Louis Pasteur first proposed the idea that the oxidation of ammonia was a biological process. As time went on, many scientists conducted in-depth research on the nitrogen cycle, and the oxidation process of nitrite was a crucial link in the cycle. It was these early explorations that led to the development of modern microbiology.
The significance of ecology
Considering that nitrogen is an important element for plant growth, the role of ammonia-oxidizing bacteria is particularly prominent in agricultural settings. When ammonia enters the soil, it is converted through the nitrogen cycle into nitrates that plants can absorb. This is especially important during the application of fertilizers because it affects the purification and loss of nitrogen. More importantly, the ammonia conversion process also plays an indispensable role in removing nitrogen from municipal wastewater, which makes ammonia-oxidizing bacteria play an important role in environmental science.
Future challenges
As environmental problems intensify around the world, such as climate change and nitrogen pollution of groundwater, understanding and managing the nitrogen cycle has become an important current issue. The ability of ammonia-oxidizing bacteria to adapt to nitrogen cycling in extreme environments provides important clues for future ecosystem restoration and design. At the same time, how to effectively select ammonia oxidation inhibitors to reduce nitrogen loss and improve fertilizer efficiency has also become an urgent problem to be solved.
In this world of microorganisms, what changes are ammonia-oxidizing bacteria leading to, and how will they affect our future?
