Author: Nikki Jiang
Editors: Peggy Yang and Angela Lin
Artist: Aurora Chen
Similar to the water cycle, nitrogen also cycles in nature with the help of different types of bacteria. About 78% of the air in the Earth’s atmosphere is made up of nitrogen meaning that it is very abundant. With the help of the nitrogen cycle, nitrogen can exist in soil, water, and the air. It is the nutrient that plants need to make chlorophyll and capture sunlight. Nitrogen is also needed for proteins, DNA, and amino acids. Too much nitrogen can have side effects as well. Nitrogen-based fertilizer can cause nitrogen pollution in our water ecosystems. Even though we have a lot of nitrogen, much of it is in the gaseous form (N2) which cannot be used by living organisms. That is where the nitrogen cycle comes in to convert this unusable form of nitrogen into something usable.
Nitrogen fixation, nitrification, and denitrification are the three main processes in the nitrogen cycle. All of the bacteria used in the nitrogen cycle contain special enzymes that allow them to do their role in the cycle. Nitrogen-fixing bacteria convert nitrogen gas to ammonium and/or nitrate which can be used by plants. This type of bacteria can be found in soil or nodes in the roots of legumes. Bacillus, clostridium, rhizobium, and azotobacter are all examples of nitrogen-fixing bacteria. A special enzyme in these bacteria called nitrogenase allows for the conversion to ammonium; which is a nutrient used by plants. Bacteria play a big role in the nitrogen cycle.
Nitrifying bacteria can either convert ammonium to nitrite through oxidation or convert nitrite to nitrate. Through this oxidation process, energy is obtained for nitrifying bacteria. Special enzymes, monooxygenase and nitrite oxidoreductase in the bacteria allows the nitrification process to occur.
The process of denitrification completes the cycle where nitrates are converted back to nitrogen gas. Although nitrate and nitrite are essential nutrients to maintain the well-being of plants, there can be an excess of nitrate in the soil. Denitrifying bacteria are necessary to prevent the accumulation of nitrogen in the water. By releasing the nitrogen as gas, it can re-enter the soil and be reused by plants. The nitrogen cycle is not complete without denitrifying bacteria. Some examples include the pseudomonas family denitrificans. These bacteria have the enzymes nitric oxide reductase, nitrite reductase, and nitrate reductase. The nitrogen cycle is dependent on bacteria to convert and recycle all forms of nitrogen.
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