Related Research Articles
Rhizobia are diazotrophic bacteria that fix nitrogen after becoming established inside the root nodules of legumes (Fabaceae). To express genes for nitrogen fixation, rhizobia require a plant host; they cannot independently fix nitrogen. In general, they are gram negative, motile, non-sporulating rods.
Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium species form an endosymbiotic nitrogen-fixing association with roots of legumes and Parasponia.
Sinorhizobium meliloti is a Gram-negative bacterium which fixes atmospheric nitrogen. It forms a symbiotic relationship with legumes from the genera Medicago, Melilotus and Trigonella, including the model legume Medicago truncatula. This symbiosis results in a new plant organ termed a root nodule and is deemed symbiotic as it leaves excess nitrogen behind for the plant. S. meliloti are mobile and possess a cluster of peritrichous flagella. The S. meliloti genome contains four genes coding for flagellin. These include fliC1C2–fliC3C4. The genome contains three replicons: a chromosome, a chromid, and a plasmid. Individual strains may possess additional, accessory plasmids. Five S. meliloti genomes have been sequenced to date: Rm1021, AK83, BL225C, Rm41, and SM11 with 1021 considered to be the wild type.
Root nodules are found on the roots of plants, primarily legumes, that form a symbiosis with nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known as rhizobia. This process has evolved multiple times within the legumes, as well as in other species found within the Rosid clade. Legume crops include beans, peas, and soybeans.
Nod factors, are signaling molecules produced by soil bacteria known as rhizobia in response to flavonoid exudation from plants under nitrogen limited conditions. Nod factors initiate the establishment of a symbiotic relationship between legumes and rhizobia by inducing nodulation. Nod factors produce the differentiation of plant tissue in root hairs into nodules where the bacteria reside and are able to fix nitrogen from the atmosphere for the plant in exchange for photosynthates and the appropriate environment for nitrogen fixation. One of the most important features provided by the plant in this symbiosis is the production of leghemoglobin, which maintains the oxygen concentration low and prevents the inhibition of nitrogenase activity.
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 (N2); they must use nitrogen compounds such as nitrates.
Sinorhizobium/Ensifer is a genus of nitrogen-fixing bacteria (rhizobia), three of which have been sequenced.
Bradyrhizobium japonicum is a species of legume-root nodulating, microsymbiotic nitrogen-fixing bacteria. The species is one of many Gram-negative, rod-shaped bacteria commonly referred to as rhizobia. Within that broad classification, which has three groups, taxonomy studies using DNA sequencing indicate that B. japonicum belongs within homology group II.
Pararhizobium giardinii is a Gram negative root nodule bacteria. It forms nitrogen-fixing root nodules on legumes, being first isolated from those of Phaseolus vulgaris.
Mesorhizobium tianshanense, formerly known as Rhizobium tianshanense, is a Gram negative species of bacteria found in the root nodules of many plant species. Its type strain is A-1BS.
Mesorhizobium plurifarium is a species of root nodule bacteria first isolated from Acacia species in Senegal. Its type strain is ORS 1032.
Bradyrhizobium yuanmingense is a species of legume-root nodulating, endosymbiont nitrogen-fixing bacterium, associated with Lespedeza and Vigna species. Its type species is CCBAU 10071(T).
Mesorhizobium ciceri is a gram-negative, nitrogen-fixing motile bacteria from the genus of Mesorhizobium which was isolated from Chickpea nodules of Cicer arietinum in Spain. Rhizobium cicero was transferred to Mesorhizobium ciceri.
Mesorhizobium huakuii is a bacterium from the genus Mesorhizobium which was isolated from the legume Astragalus sinicus in Nanjing in China. Rhizobium huakuii was transferred to Mesorhizobium huakuii.
Mesorhizobium mediterraneum is a bacterium from the genus Mesorhizobium, which was isolated from root nodule of the Chickpea in Spain. The species Rhizobium mediterraneum was subsequently transferred to Mesorhizobium mediterraneum. This species, along with many other closely related taxa, have been found to promote production of chickpea and other crops worldwide by forming symbiotic relationships.
Rhizobium lusitanum is a Gram negative root nodule bacteria, specifically nodulating Phaseolus vulgaris. Its type strain is P1-7T.
Rhizobium loessense is a root nodule bacteria, first isolated from nodules of Astragalus and Lespedeza species. Its type strain is CCBAU 7190BT.
Rhizobium bangladeshense is a gram-negative bacterium which was isolated from root nodules of lentils in Bangladesh.
Rhizobium lentis is a gram-negative bacterium which was isolated from root nodules of lentils in Bangladesh.
A symbiosome is a specialised compartment in a host cell that houses an endosymbiont in a symbiotic relationship.
References
- ↑ Chen, W.-X.; Tan, Z.-Y.; Gao, J.-L.; Li, Y.; Wang, E.-T. (1997). "Rhizobium hainanense sp. nov., Isolated from Tropical Legumes". International Journal of Systematic Bacteriology. 47 (3): 870–873. doi: 10.1099/00207713-47-3-870 . ISSN 0020-7713. PMID 9226920.
