Rhizobium

Rhizobium is a bacterium that has good as well as bad effects on plants, animals, and the environment. It is a group of bacteria, some are very useful for us whereas some are pathogenic. Rhizobium is known to be a very good symbiote, symbiotic relationship between leguminous plants and rhizobium plays a very important role in our environment. Diseases caused by rhizobium are so hard to cure, do you know why it is so? We will talk more about Rhizobium in this article.

What is Rhizobium?

Rhizobium is a group of bacteria. The word rhizobium refers to the genus of various species that come under this group such as Rhizobium leguminous, Rhizobium alamii, and Rhizobium eguminosarum. It’s a gram-negative soil bacteria that is present in the roots of leguminous plants. It was first cultivated and isolated by Martinus Beisernick in 1888.

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Role of Rhizobium

Rhizobium is a versatile microorganism that plays various roles in different aspects such as the environment, plants animals, etc. But one of the most important roles it plays is Nitrogen Fixation. Which is nothing but conversion of atmospheric nitrogen into usable compounds. Before digging more about this topic lets understand why we need to fix nitrogen.

What is Nitrogen Fixation?

Nitrogen fixation is a phenomenon in which atmospheric nitrogen is converted into usable compounds such as ammonia . That can occur only in leguminous plants such as pea or bean plants. Rhizobium attaches to the root of a leguminous plant and stimulates biological nitrogen fixation. Which is briefly explained below.

Once nitrogen is converted into usable compounds (ammonia), it can be utilized by plants from the soil through their roots. Nitrogen is then used for the synthesis of plant proteins and other compounds. Animals feeding on plants get these proteins and other nitrogen compounds. It helps in maintaining atmospheric nitrogen content by nitrogen fixing cycle .

Why Nitrogen Fixation?

Our atmosphere has 78% nitrogen gas. Rhizobium are known to form symbiotic relationships with leguminous plants (plants give organic compounds made by photosynthesis ,in return bacteria fix nitrogen for the plant ) . Nitrogen is one of the essential constituents of all living organisms as part of proteins, chlorophyll, nucleic acids and vitamins. Nitrogen cannot be taken directly by plants and animals to convert nitrogen into usable form there is a phenomenon called fixation which occurs in leguminous plants only.

Classification of Rhizobium

Rhizobium are single celled usually rod shaped bacteria of 0.8 – 2.0 micro units .It often has flagella .Rhizobium attach to the roots of leguminous plants which gives a nodule-like appearance called root nodule. Classification of Rhizobium is given below:

1. Kingdom: Monera
2. Order: Rizobiales
3. Family: Rizobiaceae
4. Genus: Rhizobium

Benefits of Rhizobium

Following are the benefits provided by rhizobium are given below:

• Rhizobium acts as a biofertilizer.
• Providing nitrogen to the leguminous plant and hence considered as a very important process for enhancing yield and soil fertility.
• Rhizobium has been used in organic farming to stimulate growth of roots , protection from soil-borne pathogens and improve stress tolerance.
• Research is being conducted by scientists to find a way to use Rhizobium’s biological nitrogen fixation.

Disease Caused by Rhizobium

While Rhizobia plays a crucial role in enhancing plant growth by facilitating nitrogen fixation, it’s important to be aware that certain strains can also act as pathogens, potentially leading to detrimental effects on plant health. Some species of Rhizobia such as Rhizobium rhizogenes and Rhizobium radiobium cause serious disease in plants . Since it is gram negative bacteria its cell wall contains a thin layer of peptidoglycan and lipoprotein which make them resistant to drugs and antibiotics .

FAQ’s – Rhizobium

1. Nitrogen fixation can only be performed by the rhizobium bacteria?

No, nitrogen fixation can be performed by other bacteria such as Azotobacter, cyanobacterium. But Rhizobium is the only bacterium that fixes nitrogen by engaging in a symbiotic relationship with leguminous plants.

2. Do all Species of Rhizobium Fix Nitrogen?

No, only a few of them can fix nitrogen, as it mentioned above not all rhizobium is good for plants and animals, some of them can also cause diseases. Since rhizobium are gram negative bacteria they have high antibiotic tolerance.

3. What is a Symbiotic Relationship?

It’s a phenomenon where two organisms from different species live together in order to fulfill each other’s needs .For example, the relation between rhizobium and leguminous plants, plants give food to bacteria and in return rhizobium convert or fix nitrogen into usable form for plants .

4. What kind of Disease in Plants is Caused by Rhizobium ?

Few diseases caused by rhizobium in plants are hair root disease in dicots , crown gall disease etc.

5. What is biofertilizer?

Biofertilizers are the microorganisms when used in farming in order to provide required nutrients to the soil to increase yield. Rhizobium are one of those biofertilizers that give nitrogen to soil .

6. How Rhizobium helps in Improving Soil Quality?

Rhizobium acts as a biofertilizer in the agricultural field, it is present in the root of leguminous plants providing nitrogen to the soil and hence enhancing the soil yield and quality.

7. What makes Gram Bacteria have High Antibiotic Resistance?

Gram negative bacteria consists of following layers which makes it high antibiotic resistance :

• It has an outermost covering made of lipopolysaccharide.
• Two thin layers of wavy cell wall made of peptidoglycan.