Soybean root nodules, each containing billions of Bradyrhizobium bacteria

Rhizobia (from the Greek words riza = root and bios = Life) are soil bacteria that fix nitrogen (diazotrophy) after becoming established inside root nodules of legumes (Fabaceae). The rhizobia cannot independently fix nitrogen, and require a plant host. Morphologically they are generally gram negative, motile, non-sporulating rods. Image File history File links Soybean root nodules, containing billions of Rhizobium bacteria Downloaded from : [[1]] File links The following pages link to this file: Rhizobia ... Image File history File links Soybean root nodules, containing billions of Rhizobium bacteria Downloaded from : [[1]] File links The following pages link to this file: Rhizobia ... SOiL is a five-piece aggressive rock/Nu Metal band from Chicago, formed in 1997 by ex-members of renowned death metal acts Broken Hope and Oppressor. ... Phyla/Divisions Actinobacteria Aquificae Bacteroidetes/Chlorobi Chlamydiae/Verrucomicrobia Chloroflexi Chrysiogenetes Cyanobacteria Deferribacteres Deinococcus-Thermus Dictyoglomi Fibrobacteres/Acidobacteria Firmicutes Fusobacteria Gemmatimonadetes Nitrospirae Omnibacteria Planctomycetes Proteobacteria Spirochaetes Thermodesulfobacteria Thermomicrobia Thermotogae Bacteria (singular, bacterium) are a major group of living organisms. ... Nitrogen fixation is the process by which nitrogen is taken from its relatively inert molecular form (N2) in the atmosphere and converted into nitrogen compounds useful for other chemical processes (such as, notably, ammonia, nitrate and nitrogen dioxide). ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... Diazotrophs are microorganisms that fix atmospheric nitrogen gas in to a more usable form such as ammonia. ... Root nodules occur on the roots of plants that associate with symbiotic bacteria. ... Subfamilies Faboideae Caesalpinioideae Mimosoideae References GRIN-CA 2002-09-01 The name Fabaceae belongs to either of two families, depending on viewpoint. ... Gram-positive anthrax bacteria (purple rods) in cerebrospinal fluid sample. ...

History

The first species (R. leguminosarum) was identified in 1889, and all further species placed in the Rhizobium genus. However, more advanced methods of analysis have revised this classification and now there are many in other genera. Rhizobium is still sometimes used as the singular of rhizobia. Most research has been done on crop and forage legumes such as clover, beans, and soy. However, recently more work is occurring on indigenous legumes. 1889 (MDCCCLXXXIX) was a common year starting on Tuesday (see link for calendar). ... Look up crop in Wiktionary, the free dictionary. ... Forage is the herbaceous plant material (mainly grasses and legumes) eaten by grazing animals. ... Species See text Clover (Trifolium) is a genus of about 300 species of plants in the pea family Fabaceae. ... Green beans Bean is a common name for large plant seeds of several genera of Fabaceae (formerly Leguminosae) used for food or feed. ... Binomial name Glycine max Soybeans (US) or soya beans (UK) (Glycine max) are a high-protein legume (Family Fabaceae) grown as food for both humans and livestock. ... The word indigenous is an adjective derived from the Latin word indigena, meaning native, belonging to, aboriginal; and has several applications: Indigenous peoples, communities and cultures native or indigenous to a territory; Indigenous (band), a Native American blues-rock band; In biology, indigenous means native to a place or biota...

Taxonomy

Rhizobia consist of 55 species found in 12 genera^[1]. Most belong to the Rhizobiales, a probably-monophyletic group of proteobacteria. Within that group, however, they are scattered among several different families: Families Aurantimonadaceae Bartonellaceae Beijerinckiaceae Bradyrhizobiaceae Brucellaceae Hyphomicrobiaceae Methylobacteriaceae Methylocystaceae Phyllobacteriaceae Rhizobiaceae Rhodobiaceae The Rhizobiales are an order of alpha proteobacteria. ... In phylogenetics, a group is monophyletic (Greek: of one stem) if all organisms in that group are known to have developed from a common ancestral form, and all descendants of that form are included in the group. ... Orders Alpha Proteobacteria    Caulobacterales - e. ...

These groups also include a variety of other bacteria. For instance, the plant pathogen Agrobacterium is a closer relative of Rhizobium than the rhizobia that nodulate soybean (and may not really be a separate genus). The genes responsible for the symbiosis with plants, however, may be closer than the organisms themselves, acquired by horizontal transfer rather than from a common ancestor. Genera Agrobacterium Rhizobium Sinorhizobium Ensifer The Rhizobiaceae are a family of proteobacteria, including many (but not all) species of rhizobia as well as plant parasites like Agrobacterium. ... ENSIFER (plural ENSIFERI) is a Latin word, meaning carrier (or user) of a sword It has different meaning: in history, a member of the Livonian military order of the Schwertbrüder (German word, meaning Swordbrethren, but also rendered as Swordbearers) in zoology, a genus of the bacterial family of Rhizobiaceae... Genera Afipia Agromonas Blastobacter Bosea Bradyrhizobium Nitrobacter Oligotropha Photorhizobium Rhodoblastus Rhodopseudomonas The Bradyrhizobiaceae are a family of bacteria, with ten genera. ... Genera Ancalomicrobium Ancylobacter Angulomicrobium Aquabacter Azorhizobium Blastochloris Devosia Dichotomicrobium Filomicrobium Gemmiger Hyphomicrobium Labrys Methylorhabdus Pedomicrobium Prosthecomicrobium Rhodomicrobium Rhodoplanes Seliberia Starkeya Xanthobacter The Hyphomicrobiaceae are a family of bacteria. ... Genera Aminobacter Aquamicrobium Defluvibacter Hoeflea Mesorhizobium Nitratireductor Parvibaculum Phyllobacterium Pseudaminobacter The Phyllobacteriaceae are a family of bacteria that contain nine genera. ... Genera Brucella Mycoplana Ochrobactrum The Brucellaceae are a family of Rhizobiales. ... Genera Methylobacterium Microvirga Protomonas Roseomonas The Methylobacteriaceae are a family of Rhizobiales. ... Genera Burkholderia Cupriavidus Lautropia Thermothrix The Burkholderiaceae are a family of bacteria, included in the order Burkholderiales. ... Species Burkholderia ambifaria Burkholderia andropogonis Burkholderia anthina Burkholderia brasilensis Burkholderia caledonica Burkholderia caribensis Burkholderia caryophylli Burkholderia cenocepacia Burkholderia cepacia Burkholderia cepacia complex Burkholderia dolosa Burkholderia fungorum Burkholderia gladioli Burkholderia glathei Burkholderia glumae Burkholderia graminis Burkholderia hospita Burkholderia kururiensis Burkholderia mallei Burkholderia multivorans Burkholderia phenazinium Burkholderia phymatum Burkholderia phytofirmans Burkholderia plantarii... Genera Duganella Herbaspirillum Janthinospirillum Massilia Oxalobacter Telluria The Oxalobacteraceae are a family of bacteria, included in the order Burkholderiales. ... Species Agrobacterium tumefaciens Agrobacterium rhizogenes Agrobacterium is a genus of bacteria that cause tumors in plants. ... This stylistic schematic diagram shows a gene in relation to the double helix structure of DNA and to a chromosome (right). ... Common Clownfish (Amphiprion ocellaris) in their Magnificent sea anemone (Heteractis magnifica) home. ... Horizontal gene transfer (HGT), also Lateral gene transfer (LGT) is any process in which an organism transfers genetic material (i. ... A group of organisms is said to have common descent if they have a common ancestor. ...

Importance in agriculture

Although much of the nitrogen is removed when protein-rich grain or hay is harvested, significant amounts can remain in the soil for future crops. This is especially important when nitrogen fertilizer is not used, as in organic rotation schemes or some less-industrialized countries. Nitrogen is the most commonly deficient nutrient in many soils around the world and it is the most commonly supplied plant nutrient. Supply of Nitrogen through fertilizers has severe environmental concerns. Nitrogen fixation by Rhizobium is very beneficial for environment also. A representation of the 3D structure of myoglobin, showing coloured alpha helices. ... spreading manure, an organic fertiliser Fertilizers or fertilisers are compounds given to plants with the intention of promoting growth; they are usually applied either via the soil, for uptake by plant roots, or by foliar feeding, for uptake through leaves. ... Organic cultivation of mixed vegetables in Capay, California. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... Fertilizers are chemicals given to plants with the intention of promoting growth; they are usually applied either via the soil or by foliar spraying. ... Nitrogen fixation is the process by which nitrogen is taken from its relatively inert molecular form (N2) in the atmosphere and converted into nitrogen compounds useful for other chemical processes (such as, notably, ammonia, nitrate and nitrogen dioxide). ...

Symbiosis

Rhizobia are unique because they live in a symbiotic relationship with legumes. Common crop and forage legumes are peas, beans, clover, and soy. rhizobia live in the soil where they encounter the root of a legume, if that bacteria has the correct nod or nodulating genes, symbiosis can occur. The rhizobia enter a root hair and travel down a tube to the centre of the root hair cell. Here proliferating plant cells form a nodule. The bacteria differentiate morphologically into bacteroids and fix nitrogen from the atmosphere in to a plant usable form. In return the plant feeds the bacteria with sugars, proteins, and oxygen.

The legume–Rhizobia symbiosis is a classic example of mutualism — rhizobia supply ammonia or amino acids to the plant and in return receive organic acids (principally as the dicarboxylic acids malate and succinate) as a carbon and energy source — but its evolutionary persistence is actually somewhat surprising. Because several unrelated strains infect each individual plant, any one strain could redirect resources from nitrogen fixation to its own reproduction without killing the host plant upon which they all depend. But this form of cheating should be equally tempting for all strains, a classic tragedy of the commons. It turns out that legume plants guide the evolution of rhizobia towards greater mutualism by reducing the oxygen supply to nodules that fix less nitrogen, thereby reducing the frequency of cheaters in the next generation. Common Clownfish (Amphiprion ocellaris) in their Magnificent sea anemone (Heteractis magnifica) home. ... In biology, mutualism is an interaction between two species in which both species derive benefit. ... Nitrogen fixation is the process by which nitrogen is taken from its relatively inert molecular form (N2) in the atmosphere and converted into nitrogen compounds useful for other chemical processes (such as, notably, ammonia, nitrate and nitrogen dioxide). ... The tragedy of the commons is a phrase used to refer to a class of phenomena that involve a conflict for resources between individual interests and the common good. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance transparent (gas) very pale blue (liquid) Atomic mass 15. ...

Other diazotrophs

Many other species of bacteria are able to fix nitrogen (diazotrophs), including Frankia which is symbiotic and Azospirillum which is free-living. Diazotrophs are microorganisms that fix atmospheric nitrogen gas in to a more usable form such as ammonia. ... Species Frankia alni Frankia is a genus of nitrogen fixing filamentous bacteria that live in symbiosis with actinorhizal plants, similar to Rhizobia. ...

External links

• Legume sanctions maintain Rhizobium mutualism
• Current list of rhizobia species
• Nitrogen Fixation and Inoculation of Forage Legumes

References

1. ^ Current taxonomy of rhizobia. Retrieved on 2006-08-07.