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Sinorhizobium meliloti

Sinorhizobium meliloti

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Sinorhizobium meliloti is a Gram-negative
Gram staining
Gram staining is a method of differentiating bacterial species into two large groups ....

 nitrogen-fixing
Nitrogen fixation
Nitrogen fixation is the natural process, either biological or abiotic, by which nitrogen in the atmosphere is converted into ammonia . This process is essential for life because fixed nitrogen is required to biosynthesize the basic building blocks of life, e.g., nucleotides for DNA and RNA and...

 bacterium (rhizobium
Rhizobium
Rhizobium is a genus of Gram-negative soil bacteria that fix nitrogen. Rhizobium forms an endosymbiotic nitrogen fixing association with roots of legumes and Parasponia....

). It forms a symbiotic relationship with legumes from the genera Medicago
Medicago
Medicago is a genus of flowering plants, commonly known as medick or burclover. The name is based on Latin medica 'alfalfa, lucerne,' from 'Median .'...

, Melilotus and Trigonella
Trigonella
Trigonella is a genus from the family Fabaceae. The best known member is the herb Fenugreek.-Species:The genus Trigonella currently has 37 recognized species:* Trigonella anguina Delile* Trigonella arabica Delile...

, including the model legume Medicago truncatula
Medicago truncatula
Medicago truncatula is a small legume native to the Mediterranean region that is used in genomic research. It is a low-growing, clover-like plant 10–60 cm tall with trifoliate leaves. Each leaflet is rounded, 1–2 cm long, often with a dark spot in the center...

. This symbiosis results in a new plant organ termed a root nodule
Root nodule
Root nodules occur on the roots of plants that associate with symbiotic nitrogen-fixing bacteria. Under nitrogen-limiting conditions, capable plants form a symbiotic relationship with a host-specific strain of bacteria known as rhizobia...

. The S. meliloti genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....

 contains three replicons
Replicon (genetics)
A replicon is a DNA molecule or RNA molecule, or a region of DNA or RNA, that replicates from a single origin of replication.For most prokaryotic chromosomes, the replicon is the entire chromosome. One notable exception found comes from archaea, where two Sulfolobus species have been shown to...

: a chromosome (3.65 megabases) and two chromids, pSymA (1.35 megabases) and pSymB (1.68 megabases), that have all been fully sequenced.

Nitrogen fixation by S meliloti is interfered with by the plastic modifier bisphenol A
Bisphenol A
Bisphenol A is an organic compound with two phenol functional groups. It is used to make polycarbonate plastic and epoxy resins, along with other applications....

.

Symbiosis


The symbiosis between S. meliloti and its plant hosts begins when the plant secretes an array of betaines and flavonoid
Flavonoid
Flavonoids , are a class of plant secondary metabolites....

s into the rhizosphere: 4,4'-dihydroxy-2'-methoxychalcone
Dihydrochalcone
Dihydrochalcone is a chemical compound related to chalcone.Dihydrochalcones Dihydrochalcone (DHC) is a chemical compound related to chalcone.Dihydrochalcones Dihydrochalcone (DHC) is a chemical compound related to chalcone.Dihydrochalcones (3′,5′-dihydroxy-2′,4′,6′-trimethoxydihydrochalcone,...

, chrysoeriol, cynaroside
Cynaroside
Cynaroside is a flavone, a flavonoid-like chemical compound. It is a 7-O-glucoside of luteolin and can be found in dandelion coffee, in Ferula varia and F. foetida in Campanula persicifolia and C...

, 4',7-dihydroxyflavone, 6′′-O-malonylononin, liquiritigenin, luteolin
Luteolin
Luteolin is a yellow crystalline compound. It is a flavonoid; to be specific, it is one of the more common flavones. From preliminary research, it is thought to play a role in the human body possibly as an antioxidant, a free radical scavenger, a promoter of carbohydrate metabolism, or an immune...

, 3',5-dimethoxyluteolin
Luteolin
Luteolin is a yellow crystalline compound. It is a flavonoid; to be specific, it is one of the more common flavones. From preliminary research, it is thought to play a role in the human body possibly as an antioxidant, a free radical scavenger, a promoter of carbohydrate metabolism, or an immune...

, 5-methoxyluteolin
Luteolin
Luteolin is a yellow crystalline compound. It is a flavonoid; to be specific, it is one of the more common flavones. From preliminary research, it is thought to play a role in the human body possibly as an antioxidant, a free radical scavenger, a promoter of carbohydrate metabolism, or an immune...

, medicarpin
Medicarpin
Medicarpin is a pterocarpan, a derivative of isoflavonoids, found in Medicago truncatula.The root nodule formation by Sinorhizobium meliloti is apparently dependent on the flavonoids pathway.-Metabolism:...

, stachydrine, trigonelline
Trigonelline
Trigonelline is an alkaloid with chemical formula 772. It is an inner salt formed by the addition of a methyl group to the nitrogen atom of niacin...

. These compounds attract S. meliloti to the surface of the root hairs of the plant where the bacteria begin secreting nod factor
Nod factor
Nodulation factors are signaling molecules produced by bacteria known as rhizobia during the initiation of nodules on the root of legumes. A symbiosis is formed when legumes take up the bacteria...

.

Bacteriophage


Several bacteriophage
Bacteriophage
A bacteriophage is any one of a number of viruses that infect bacteria. They do this by injecting genetic material, which they carry enclosed in an outer protein capsid...

s have been described which infect Sinorhizobium meliloti: Φ1, Φ1A, Φ2A, Φ3A, Φ4 (=ΦNM8), Φ5t (=ΦNM3), Φ6 (=ΦNM4), Φ7 (=ΦNM9), Φ7a, Φ9 (=ΦCM2), Φ11 (=ΦCM9), Φ12 (=ΦCM6), Φ13, Φ16, Φ16-3, Φ16a, Φ16B, Φ27, Φ43, Φ70, Φ2011, ΦA3, ΦA8, ΦA161, ΦAL1, ΦCM1, ΦCM3, ΦCM4, ΦCM5, ΦCM7, ΦCM8, ΦCM20, ΦCM21, ΦDF2, Φf2D, ΦF4, ΦFAR, ΦFM1, ΦK1, ΦL1, ΦL3, ΦL5, ΦL7, ΦL10, ΦL20, ΦL21, ΦL29, ΦL31, ΦL32, ΦL53, ΦL54, ΦL55, ΦL56, ΦL57, ΦL60, ΦL61, ΦL62, ΦLO0, ΦLS5B, ΦM1, ΦM1, ΦM1-5, ΦM2, ΦM3, ΦM4, ΦM5, ΦM5 (=ΦF20), ΦM5N1, ΦM6, ΦM7, ΦM8, ΦM9, ΦM10, ΦM11, ΦM11S, ΦM12, ΦM14, ΦM14S, ΦM19, ΦM20S, ΦM23S, ΦM26S, ΦM27S, ΦMl, ΦMM1C, ΦMM1H, ΦMP1, ΦMP2, ΦMP3, ΦMP4, ΦN2, ΦN3, ΦN4, ΦN9, ΦNM1, ΦNM2, ΦNM6, ΦNM7, ΦP6, ΦP10, ΦP33, ΦP45, ΦPBC5, ΦRm108, ΦRmp36A, ΦRmp38, ΦRmp86, ΦSP, ΦSSSS304, ΦSSSS305, ΦSSSS307, ΦSSSS308, and ΦT1.

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