Aquatic Root Nodules

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Kingdom: Eubacterium
Image Courtesy of: Dazzo, Frank
Image Width: 4.7 microns
Image Technology: TEM (Transmission Electron Microscope)

This view shows microbes inside the root of an aquatic plant. These bacteria form "symbiosomes" of bacteroids which are inside the root nodules of an aquatic plant, Neptunia. Root nodules form when a type of bacterium, rhizobium, infects the plant's roots. This "infection" is not harmful to the plant, and is not the source of a disease. 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. In return, the rhizobia "fix" nitrogen for the plant. What does "fixing" nitrogen mean? 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. Nitrogen is found in all living creatures. It is one of the key components of proteins, which are the structural building blocks of living cells. The process of extracting nitrogen from air and combining it with other compounds to form proteins is called "nitrogen fixation". Since plants cannot fix nitrogen themselves, they are dependent on these nitrogen fixing bacteria for the proteins that they need to survive and grow.