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Some nitrogen-fixing bacteria have symbiotic relationships with plants, especially legumes, mosses and aquatic ferns such as Azolla. [4] Looser non-symbiotic relationships between diazotrophs and plants are often referred to as associative, as seen in nitrogen fixation on rice roots. Nitrogen fixation occurs between some termites and fungi. [5]
Sulphate-reducing bacteria are important in ocean sediments (e.g. Desulfovibrio), and some Archean methanogens, like Methanococcus, fix nitrogen in muds, animal intestines [3] and anoxic soils. [4] Facultative anaerobes—these species can grow either with or without oxygen, but they only fix nitrogen anaerobically.
Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitrogen-fixing association with roots of (primarily) legumes and other flowering plants. The bacteria colonize plant cells to form root nodules, where they convert atmospheric nitrogen into ammonia using the enzyme nitrogenase.
To express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen. [1] In general, they are gram negative, motile, non-sporulating rods. Rhizobia are a "group of soil bacteria that infect the roots of legumes to form root nodules". [2]
The nitrogen-fixing clade consists of four orders of flowering plants: Cucurbitales, Fabales, Fagales and Rosales. [a] This subgroup of the rosids encompasses 28 families of trees, shrubs, vines and herbaceous perennials and annuals. The roots of many of the species host bacteria that fix nitrogen into compounds the plants can use. [4] [5]
Bradyrhizobium is a genus of Gram-negative soil bacteria, many of which fix nitrogen. Nitrogen fixation is an important part of the nitrogen cycle. Plants cannot use atmospheric nitrogen (N 2); they must use nitrogen compounds such as nitrates.
Heterocysts abandon oxygen-producing photosynthesis in order to fix nitrogen with the oxygen-sensitive enzyme nitrogenase. Vegetative and heterocyst cells divide labor by exchanging sugars and nitrogen. The bacteria may also enter a symbiotic relationship with certain plants. In such a relationship, the bacteria do not respond to the ...
The host plant provides the bacteria with amino acids so they do not need to assimilate ammonia. [5] The amino acids are then shuttled back to the plant with newly fixed nitrogen. Nitrogenase is an enzyme involved in nitrogen fixation and requires anaerobic conditions. Membranes within root nodules are able to provide these conditions.