How Do Nitrifying Bacteria Impact the Nitrogen Cycle?
The nitrifying bacteria name is the plural of the nitrifying bacterium. They are a small group of aerobic bacteria from the family named Nitrobacteraceae which uses inorganic chemicals as the source of energy. Nitrifying bacteria are microorganisms that play a very vital role in the nitrogen cycle as converters of soil ammonia to nitrates.
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The process of nitrification, involves two different groups of bacteria, one that converts ammonia to nitrites (Nitrosomonas, Nitrosospira, Nitrosococcus, and Nitrosolobus) and the other to convert nitrites to nitrates (Bacteria Nitrobacter, Nitrospina, and Nitrococcus). In the process of agriculture, irrigation if the solution is diluted with ammonia results in an increase in the soil nitrates, through the action of nitrifying bacteria.
Nitrogen Cycle
It is a biogeochemical process, in which nitrogen is converted into different forms. It is a continuous process of passing nitrogen from the atmosphere to the soil and later to the organisms and then back into the atmosphere. The nitrogen process involves several processes like nitrogen fixation, nitrification, denitrification, decay, and putrefaction.
Nitrogen gas exists in two forms organic and inorganic, in which organic nitrogen exists in the living organisms, which gets passed to the other living organisms through the food chain. The inorganic form of nitrogen is found in the atmosphere in abundance, which is available to plants by symbiotic bacteria that can be converted into inert nitrogen into a usable form like nitrites and nitrates.
To maintain balance in the ecosystem nitrogen undergoes various types of transformations and furthermore, this process extends to various biomes, with the marine cycle being one of the most biogeochemical cycles.
Stages of Nitrogen Cycle
The different stages of the nitrogen cycles are – Nitrogen fixation, Nitrification, Assimilation, Ammonification, and Denitrification, these are discussed in detail below.
Nitrogen Fixation
This is the initial step of the nitrogen cycle, in this process atmospheric nitrogen which is in inert form is converted into ammonia usable form.
The nitrogen gas is present in the inert form and it is deposited into the soil from the atmosphere and surface waters during this process, through precipitation. In this process, it undergoes a set of changes, where nitrogen atoms will get separated and combine with hydrogen to form ammonia.
The nitrogen fixation is entirely completed by symbiotic bacteria which are known as Diazotrophs. Azotobacter and Rhizobium also have a major role in this process, as these bacteria consist of a nitrogenase enzyme that has the capability to combine gaseous nitrogen with hydrogen to form ammonia.
Nitrogen fixation can occur through atmospheric fixation which involves lightening or industrial fixation by manufacturing ammonia under high temperature and pressure conditions. Nitrogen can also be fixed by man-made processes, primarily industrial processes that create ammonia and nitrogen-rich fertilizers.
Types of Nitrogen Fixation:
Atmospheric Fixation: It is a natural phenomenon where the energy of lightning breaks the nitrogen into nitrogen oxides and is then used by plants.
Industrial Nitrogen Fixation: This is a man-made alternative that helps in nitrogen fixation by the use of ammonia, it is produced by the direct combination of nitrogen and hydrogen.
Biological Nitrogen Fixation: As the nitrogen is not directly usable from the air to plants and animals. Some of the bacterias such as Rhizobium and blue-green algae transform the unusable form of nitrogen into other compounds that are more readily usable.
Nitrification
In the process of bacteria nitrification, ammonia is converted into nitrate with the presence of bacteria in the soil, nitrites are formed by the oxidation of ammonia with the help of Nitrosomonas bacteria species. further, the produced nitrites are converted into nitrates with the help of Nitrobacter bacteria, this conversion is very important as ammonia gas is very toxic for plants.
The process of bacteria nitrification involves the following reaction:
2NH4+ + 3O → 2NO2- + 4H+ + 2H2O
2NO2- + O2 → 2NO3-
Assimilation
Some of the primary producers like plants take nitrogen compounds directly from the soil, with the help of their roots. which are available in the form of ammonia, nitrite ions, nitrate ions, or ammonia ions, and they are used in the formation of the plant proteins, in this way they enter the food web when the primary consumer eat the plants.
Ammonification
The nitrogen which is present in the organic matter is released back into the soil, the plants and animals die. some of the decomposers like bacteria and fungi (present in the soil), convert the organism matter back into ammonium. The ammonia produced in this process of decomposition is further used for other biological processes.
Denitrification
Denitrification is the process by which nitrogen compounds make their way back into the atmosphere by converting nitrate into gaseous nitrogen. This process is the final stage of the nitrogen cycle, which occurs in the absence of oxygen. This process is carried out by the denitrifying bacteria, some of them are Clostridium and Pseudomonas, which will process nitrate to gain oxygen and give out free nitrogen gas as a byproduct.
Difference Between Nitrifying and Denitrifying Bacteria
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What would happen to the ecosystem without nitrifying bacteria? The condition of the ecosystem will be worse, as there will be no nitrogen fixation, most of the photosynthesis process will come to a grinding halt within a year. Also, there will be no microbes to break a large amount of waste accumulated.
FAQs on Nitrifying Bacterium: Definition, Cycle & Types
1. What are nitrifying bacteria?
Nitrifying bacteria are a specific group of aerobic microorganisms that play a vital role in the Earth's nitrogen cycle. Their primary function is to convert ammonia (NH₃), which is often toxic to plants and animals, into nitrates (NO₃⁻), a form of nitrogen that plants can easily absorb and use for growth. This entire process is known as nitrification.
2. What is the main function of nitrifying bacteria in an ecosystem?
The main function of nitrifying bacteria is to carry out nitrification. This is a crucial two-step process for making nitrogen available to plants. First, ammonia-oxidising bacteria convert ammonia into nitrites (NO₂⁻). Then, nitrite-oxidising bacteria convert these nitrites into nitrates (NO₃⁻). Nitrates are the primary source of nitrogen for most plants, making these bacteria essential for soil fertility and overall ecosystem health.
3. What are some key examples of nitrifying bacteria?
Nitrifying bacteria are classified into two main groups based on the specific step of nitrification they perform. The most common examples are:
- Ammonia-Oxidising Bacteria: These convert ammonia to nitrite. A prominent example is Nitrosomonas.
- Nitrite-Oxidising Bacteria: These convert nitrite to nitrate. A well-known example is Nitrobacter.
4. Why are nitrifying bacteria classified as chemoautotrophs?
Nitrifying bacteria are classified as chemoautotrophs because they derive their energy from chemical reactions involving inorganic compounds, not from sunlight. They oxidise inorganic nitrogen compounds (ammonia and nitrite) to produce the energy needed to live. Simultaneously, they use carbon dioxide (CO₂) from the atmosphere as their carbon source to build their cellular structures, making them 'self-feeders' (autotrophs) powered by chemicals (chemo).
5. How does the role of nitrifying bacteria differ from nitrogen-fixing bacteria like Rhizobium?
While both are crucial for the nitrogen cycle, they perform opposite functions. The key difference is:
- Nitrogen-fixing bacteria (e.g., Rhizobium) convert atmospheric nitrogen gas (N₂), which is unusable by plants, into ammonia (NH₃). This process is called nitrogen fixation.
- Nitrifying bacteria (e.g., Nitrosomonas, Nitrobacter) start with ammonia and convert it into nitrites and then nitrates. This process is nitrification.
In simple terms, nitrogen-fixers bring new, usable nitrogen into the ecosystem from the air, while nitrifiers process and recycle the nitrogen already present in the soil into a more accessible form for plants.
6. Is Azotobacter a nitrifying bacterium?
No, Azotobacter is not a nitrifying bacterium. It is a free-living (non-symbiotic) nitrogen-fixing bacterium. Its role is to convert atmospheric nitrogen (N₂) into ammonia, similar to Rhizobium, but without needing a host plant. Nitrifying bacteria, such as Nitrosomonas and Nitrobacter, perform the subsequent step of converting this ammonia into nitrates.
7. Why is the two-step process of nitrification, involving two different types of bacteria, important?
The two-step process is a form of microbial division of labour that ensures efficiency and stability. Nitrosomonas is specialised for oxidising ammonia to nitrite, and Nitrobacter is specialised for oxidising nitrite to nitrate. The intermediate product, nitrite (NO₂⁻), can be toxic to plants and other organisms at high concentrations. By having a second group of bacteria (Nitrobacter) that immediately and efficiently consumes nitrite, the ecosystem prevents its accumulation, ensuring a smooth and safe conversion to the final, useful product, nitrate (NO₃⁻).
8. What would happen to soil fertility if all nitrifying bacteria were eliminated?
If all nitrifying bacteria were eliminated, soil fertility would plummet dramatically. Ammonia from decomposition and nitrogen fixation would accumulate. Since most plants cannot efficiently use ammonia, they would suffer from nitrogen deficiency despite its presence. The accumulation of ammonia could also reach toxic levels, harming other soil microbes and plant roots. Essentially, the critical link between nitrogen waste/input (ammonia) and the most usable form of nitrogen for plants (nitrate) would be broken, leading to a collapse in plant productivity and ecosystem health.
