Close Up of Nitrogen Fixing Bacteria

Illustration Description

The illustration depicts the mechanism of how nitrogen fixing bacteria colonises roots of plants. Some nitrogen fixing bacteria such as Cyanobacteria and Azotobacter live freely in soil and water. However, one of the most important groups, the rhizobia, most live symbiotically with plant roots in order to fix nitrogen.

Rhizobia from the soil enter the roots of plants like the bean plant in the illustration. The bacteria attach to the root hairs, causing them to curl inward and form tubules called infection threads. The bacteria multiply inside the threads and move into the root tissue. The bacteria colonise the root cells, multiplying and changing their morphology into bacteroids. The expansion of the root cells forms nodules on the roots of the plant.