The Importance of Soil Microbes

As the season progresses closer to summer, folks everywhere will be utilizing the soil to grow a wide variety of plants–from flowers to crops. As I’m sure you are aware, the composition of the soil is key in producing healthy plants that grow strong. Plants require a number of macronutrients such as Hydrogen (H), Potassium (K), Nitrogen (N), Carbon (C), Oxygen (O), Phosphorus (P), and Sulfur (S) which are found in the soil. There are other elements as well that are considered important for growth, and even some micronutrients which are only required in trace amounts. With this in mind, there is another aspect to soil composition that some may not be as aware of. That is the presence of microbial life.

Microbes abound in soil. Some have established a mutualism between the host plant and itself like Rhizobium. This genera is typically found in crops like legumes. Such microbes are important to the growth of plant life because they fix nitrogen as part of the global nitrogen cycle.

They do this by taking in atmospheric nitrogen (N2) and “fixing it”. This involves the nitrogenase enzyme and a redox reaction, which turns the atmospheric nitrogen into ammonia (NH3). This ammonia is then turned into nitrites (NO2) and nitrates (NO3) which is a form of nitrogen that is usable by plants. Denitrification also occurs where eventually atmospheric nitrogen is released back into the atmosphere and the cycle begins again. As you can see, the presence of microbial life in the soil is absolutely essential.

After all, the element nitrogen is used religiously at the biochemical level. Amino acids are one such molecule. Amino acids contain an amine group (NH2), and are used to build polypeptide chains that fold into proteins. Another example would be DNA. DNA contains the four nitrogenous bases, adenine, guanine, cytosine, and thymine.

I frequently think about soil microbes, the nitrogen cycle, and its relation to plant life. It is probably the field of biology I would like to delve deeper into in graduate school. What got me thinking about it today was when I was emptying the retained water from my raised vegetable garden. The water was a yellowish-brown, and it made me wonder what nutrients were present in the water, what microbes. Naturally, I went ahead and watered other plants with this nutrient-rich water.

To conclude, I’d like to mention one genera of bacteria that I find quite fascinating. Its name is Azotobacter, a Gram-negative, free-living bacterium. This bacterium is first and foremost a diazotroph (a nitrogen fixing bacterium). It is of importance to scientists because it can fix nitrogen aerobically. It also has a neat way of protecting the sensitive nitrogenase enzyme from oxygen radicals by making a protein to protect it. Also, if conditions become rough, it will form into a cyst to prolong its survival.


Photo by: Dan H. Jones [Public Domain], via Wikimedia Commons

Remember, it’s research studying soil microbes like Azotobacter which will pave the way toward better agricultural practices, and altogether the future of our food security.

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