What is an Azotobacter?

Mary McMahon
Mary McMahon

An azotobacter is a bacterium in the genus Azotobacter, which includes at least six known species. These bacteria are found in soils all over the world, and they are free-living, living independently rather than forming symbiotic relationships with plants or other organisms. A sample of healthy soil should include a good selection of azotobacter bacteria, which can be clearly seen under the microscope and used as one criterion when evaluating soil health.

Azotobacter can be clearly seen under a microscope.
Azotobacter can be clearly seen under a microscope.

These bacteria are notable nitrogen fixers, converting free nitrogen into a form which can be used by plants. Their free-living lifestyle is somewhat unusual when compared with most other nitrogen fixing bacteria, which is one reason they are a topic of interest for scientists. Azotobacter species also have a number of potential industrial applications, with their nitrogen fixing habits being harnessed in the production of various commercial products.

Azotobacter bacteria are motile and rod-shaped. They are non-pathogenic, not causing diseases in humans and other organisms, and many species famously produce a thick slime. These bacteria are also notable for the production of large cysts which are designed to protect the bacteria when they are in a resting state. Azotobacter cysts can be clearly seen under magnification, and can be carefully sectioned to reveal the internal structures of the cyst. The cyst will not protect the bacteria from extremely harsh weather such as very high or low temperatures, but it does provide some protection, allowing the bacteria to go dormant periodically.

Some examples of Azotobacter species include A. chrococcum and A. vinelandii. Several species have been studied extensively in the lab environment to learn more about how they fix nitrogen and produce other substances of value to plants, and to discover more about the lifecycle of these bacteria and their tolerances for various environmental conditions. These bacteria can be cultured by researchers who want to develop a stock to work with, and by companies which utilize them in the production of various products.

The soil is usually teeming with bacteria, and a small soil sample can contain an astounding array of organisms. Soil health involves a very delicate balance of bacteria and organic material in the soil, and it can be easily disturbed by poor soil management practices or harsh environmental conditions. Researchers are very interested in learning more about all of the organisms involved in soil health, and determining how and why soil becomes unbalanced and unhealthy so that poor soil can be remediated.

Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


@browncoat - I've read research about azotobacter. They can be quite easily grown in a lab and are often used to research nitrogen fixation in the soil.

I don't know if they are commercially available, but it wouldn't surprise me if they were. Particularly as it must be easy to get them to go into that cyst state, which would store really well, and then just sprinkle them into the soil.

Even if they don't, the research might lead to other ways of introducing nitrogen into the soil for plants.


@pleonasm - Nitrogen fixation can be a pain as well. I know that when I moved into my new place we had a vegetable garden that had been very mismanaged and one of the first things we had to do was sow what they call a green crop.

It was of beans, because they provide food, but will also help to put some nitrogen back into the soil. And after we harvested the beans we mowed the plants into the earth.

If we had a way of putting azobacter bacteria into the soils, we wouldn't have to rely on using beans or clover as the first crop.

I can see why a commercial farmer would want to be able to do that.


I suppose the reason azotobacters are of such interest to scientists is because they don't have the limited range of other nitrogen fixing bacteria.

Other kinds of bacteria tend to be symbiotic with one particular species, or perhaps several that are similar kinds. They work pretty well together too, as the bacteria gets energy from the plant and the plant gets nitrogen that it would otherwise not be able to absorb. This is an important relationship, as nitrogen is a limiting factor for plants - they can't grow without it, and soils don't always contain it. But the bacteria can get it from the air.

Anyway, this means only certain kinds of plants can grow in soils without nitrogen. But if they can just introduce the azotobacter instead, they won't need to use nitrogen fixing plants to start off a fallow field.

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