Rhizobium Aquatic Root Nodules Click here to see a JPEG of this microbe. This view shows microbes inside the root of an aquatic plant.
Root nodules form when a type of bacterium, rhizobium, infects the plant's roots.
Once inside the plant, the rhizobia are called bacteroids. The bacteroids establish a symbiotic partnership with the plant, which is beneficial to the plant and the bacteria. The plant provides energy-rich food, produced by photosynthesis, to the rhizobia. Nitrogen, an element, is plentiful in the Earth's atmosphere. It exists there in the form of a gas, with two nitrogen atoms bound together to form a molecule.