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Ensifer meliloti (formerly Rhizobium meliloti and Sinorhizobium meliloti)<ref>Template:Cite journal</ref> are an aerobic, Gram-negative, and diazotrophic species of bacteria. S. meliloti are motile and possess a cluster of peritrichous flagella.<ref name=":0" /> S. meliloti fix atmospheric nitrogen into ammonia for their legume hosts, such as alfalfa. S. meliloti forms a symbiotic relationship with legumes from the genera Medicago, Melilotus and Trigonella, including the model legume Medicago truncatula. This symbiosis promotes the development of a plant organ, termed a root nodule. Because soil often contains a limited amount of nitrogen for plant use, the symbiotic relationship between S. meliloti and their legume hosts has agricultural applications.<ref>Template:Cite journal</ref> These techniques reduce the need for inorganic nitrogenous fertilizers.<ref>Template:Cite journal</ref>
SymbiosisEdit
Symbiosis between S. meliloti and its legume hosts begins when the plant secretes an array of betaines and flavonoids into the rhizosphere: 4,4′-dihydroxy-2′-methoxychalcone,<ref name="Maxwell" /> chrysoeriol,<ref name="Hartwig">Template:Cite journal</ref> cynaroside,<ref name="Hartwig" /> 4′,7-dihydroxyflavone,<ref name="Maxwell" /> 6′′-O-malonylononin,<ref name="Dakora">Template:Cite journal</ref> liquiritigenin,<ref name="Maxwell">Template:Cite journal</ref> luteolin,<ref>Template:Cite journal</ref> 3′,5-dimethoxyluteolin,<ref name="Hartwig" /> 5-methoxyluteolin,<ref name="Hartwig" /> medicarpin,<ref name="Dakora" /> stachydrine,<ref name="Phillips">Template:Cite journal</ref> and trigonelline.<ref name="Phillips" /> These compounds attract S. meliloti to the surface of the root hairs of the plant where the bacteria begin secreting nod factors. This initiates root hair curling. The rhizobia then penetrate the root hairs and proliferate to form an infection thread. Through the infection thread, the bacteria move toward the main root. The bacteria develop into bacteroids within newly formed root nodules and perform nitrogen fixation for the plant. A S. meliloti bacterium does not perform nitrogen fixation until it differentiates into a endosymbiotic bacteroid. A bacteroid depends on the plant for survival.<ref>Template:Cite journal</ref>
Leghemoglobin, produced by leguminous plants after colonization of S. meliloti, interacts with the free oxygen in the root nodule where the rhizobia reside. Rhizobia are contained within symbiosomes in the root nodules of leguminous plants. The leghemoglobin reduces the amount of free oxygen present. Oxygen disrupts the function of the nitrogenase enzyme in the rhizobia, which is responsible for nitrogen fixation.<ref>Template:Cite journal</ref>
GenomeEdit
The S. meliloti genome contains four genes coding for flagellin. These include fliC1C2–fliC3C4.<ref name=":0">Template:Cite book</ref> The genome contains three replicons: a chromosome (~3.7 megabases), a chromid (pSymB; ~1.7 megabases), and a plasmid (pSymA; ~1.4 megabases). Individual strains may possess additional, accessory plasmids. Five S. meliloti genomes have been sequenced to date: Rm1021,<ref>Template:Cite journal</ref> AK83,<ref name="pangenome">Template:Cite journal</ref> BL225C,<ref name="pangenome" /> Rm41,<ref>The sequence hasn't been officially announced, but is available at NCBI: chromosome, pSymA, pSymB, and pRM41a.</ref> and SM11<ref>Template:Cite journal </ref> with 1021 considered to be the wild type. Indeterminate nodule symbiosis by S. meliloti is conferred by genes residing on pSymA.<ref>Template:Cite journal</ref>
DNA repairEdit
The proteins encoded by E. meliloti genes uvrA, uvrB and uvrC are employed in the repair of DNA damages by the process of nucleotide excision repair. E. meliloti is a desiccation tolerant bacterium. However, E. meliloti mutants defective in either genes uvrA, uvrB or uvrC are sensitive to desiccation, as well as to UV light.<ref>Template:Cite journal</ref> This finding indicates that the desiccation tolerance of wild-type E. meliloti depends on the repair of DNA damages that can be caused by desiccation.
BacteriophageEdit
Several bacteriophages that infect Sinorhizobium meliloti have been described:<ref name = "Note1">Systematic naming of bacteriophages is rarely followed in the scientific literature, and a variety of phages can share the same name. While there exists an RNA phage called ΦM12, which infects enterobacteria, it is not synonymous with the DNA phage ΦM12 listed here. The same may be true for other phages in this list. Within this list, two phages have independently been named ΦM5.</ref> Φ1,<ref name = "Lesley">Template:Cite journal</ref> Φ1A,<ref name = "Staniewski">Template:Cite journal</ref> Φ2A,<ref name = "Staniewski" /> Φ3A,<ref name = "Handelsman">Template:Cite journal</ref> Φ4 (=ΦNM8),<ref name = "Werquin2"/> Φ5t (=ΦNM3),<ref name = "Werquin2"/> Φ6 (=ΦNM4),<ref name = "Werquin2"/> Φ7 (=ΦNM9),<ref name = "Werquin2"/> Φ7a,<ref name = "Lesley" /> Φ9 (=ΦCM2),<ref name = "Werquin2">Template:Cite journal and Template:Cite journal</ref> Φ11 (=ΦCM9),<ref name = "Werquin2"/> Φ12 (=ΦCM6),<ref name = "Werquin2"/> Φ13,<ref name = "Kowalski" /> Φ16,<ref name = "Kowalski" /> Φ16-3,<ref name="Ördögh">Template:Cite journal
The full genome of this phage is available at NCBI</ref> Φ16a,<ref name = "Kowalski" /> Φ16B,<ref name = "Handelsman"/> Φ27,<ref name = "Lesley" /> Φ32,<ref name="Ördögh" /> Φ36,<ref name="Ördögh" /> Φ38,<ref name="Ördögh" /> Φ43,<ref name = "Lesley" /> Φ70,<ref name = "Lesley" /> Φ72,<ref name="Ördögh" /> Φ111,<ref name="Ördögh" /> Φ143,<ref name="Ördögh" /> Φ145,<ref name="Ördögh" /> Φ147,<ref name="Ördögh" /> Φ151,<ref name="Ördögh" /> Φ152,<ref name="Ördögh" /> Φ160,<ref name="Ördögh" /> Φ161,<ref name="Ördögh" /> Φ166,<ref name="Ördögh" /> Φ2011,<ref name = "Werquin">Template:Cite journal</ref> ΦA3,<ref name = "Lesley" /> ΦA8,<ref name = "Lesley" /> ΦA161,<ref name = "Werquin"/> ΦAL1,<ref name = "Corral" /> ΦCM1,<ref name = "Werquin"/> ΦCM3,<ref name = "Werquin"/> ΦCM4,<ref name = "Werquin"/> ΦCM5,<ref name = "Werquin"/> ΦCM7,<ref name = "Werquin"/> ΦCM8,<ref name = "Werquin"/> ΦCM20,<ref name = "Werquin"/> ΦCM21,<ref name = "Werquin"/> ΦDF2,<ref name = "Corral">Template:Cite journal</ref> Φf2D,<ref name = "Corral" /> ΦF4,<ref name = "Kowalski2">Template:Cite journal</ref> ΦFAR,<ref name = "Corral" /> ΦFM1,<ref name = "Werquin"/> ΦK1,<ref>Template:Cite journal</ref> ΦL1,<ref name = "Kowalski">Template:Cite journal Note that this article was reprinted in Plant and Soil (1971) 35 (1): 63—66, which is where the URL and doi direct to.</ref> ΦL3,<ref name = "Kowalski" /> ΦL5,<ref name = "Kowalski" /> ΦL7,<ref name = "Kowalski" /> ΦL10,<ref name = "Kowalski" /> ΦL20,<ref name = "Kowalski" /> ΦL21,<ref name = "Kowalski" /> ΦL29,<ref name = "Kowalski" /> ΦL31,<ref name = "Kowalski" /> ΦL32,<ref name = "Kowalski" /> ΦL53,<ref name = "Kowalski" /> ΦL54,<ref name = "Kowalski" /> ΦL55,<ref name = "Kowalski" /> ΦL56,<ref name = "Kowalski" /> ΦL57,<ref name = "Kowalski" /> ΦL60,<ref name = "Kowalski" /> ΦL61,<ref name = "Kowalski" /> ΦL62,<ref name = "Kowalski" /> ΦLO0,<ref name = "Corral" /> ΦLS5B,<ref name = "Werquin"/> ΦM1,<ref name = "Note1" /><ref name = "Finan" /> ΦM1,<ref name = "Note1" /><ref>Template:Cite journal</ref> ΦM1-5,<ref name = "Werquin"/> ΦM2,<ref name = "Johansen">Template:Cite journal</ref> ΦM3,<ref name = "Lesley" /> ΦM4,<ref name = "Lesley" /> ΦM5,<ref name = "Note1" /><ref name = "Lesley" />
<ref name = "Johnson">Template:Cite journal</ref> ΦM5 (=ΦF20),<ref name = "Note1" /><ref name = "Finan" /> ΦM5N1,<ref name = "Werquin"/> ΦM6,<ref name = "Finan" /> ΦM7,<ref name = "Finan" /> ΦM8,<ref name = "Johansen" /> ΦM9,<ref name = "Finan" /> ΦM10,<ref name = "Finan" /> ΦM11,<ref name = "Finan" /> ΦM11S,<ref name = "Werquin"/> ΦM12,<ref name = "Finan">Template:Cite journal</ref><ref name = "Brewer">Template:Cite journal</ref> ΦM14,<ref name = "Finan" /> ΦM14S,<ref name = "Werquin"/> ΦM19,<ref>Template:Cite journal</ref> ΦM20S,<ref name = "Werquin"/><ref name = "Werquin3">Template:Cite journal</ref> ΦM23S,<ref name = "Werquin"/> ΦM26S,<ref name = "Werquin"/> ΦM27S,<ref name = "Werquin"/> ΦMl,<ref>Template:Cite journal</ref> ΦMM1C,<ref name = "Werquin"/> ΦMM1H,<ref name = "Werquin"/> ΦMP1,<ref name = "Martin">Template:Cite journal</ref> ΦMP2,<ref name = "Martin" /> ΦMP3,<ref name = "Martin" /> ΦMP4,<ref name = "Martin" /> ΦN2,<ref name = "Lesley" /> ΦN3,<ref name = "Lesley" /> ΦN4,<ref name = "Lesley" /> ΦN9,<ref name = "Lesley" /> ΦNM1,<ref name = "Werquin" /><ref name = "Werquin3" /> ΦNM2,<ref name = "Werquin" /><ref name = "Werquin3" /> ΦNM6,<ref name = "Werquin" /><ref name = "Werquin3" /> ΦNM7,<ref name = "Werquin" /><ref name = "Werquin3" /> ΦP6,<ref name = "Kowalski2" /> ΦP10,<ref name = "Kowalski2" /> ΦP33,<ref name = "Kowalski2" /> ΦP45,<ref name = "Kowalski2" /> ΦPBC5,<ref name="PBC5">This phage has never been formally reported in the scientific literature. However, the full genomic sequence has been uploaded to NCBI, available here.</ref> ΦRm108,<ref>Template:Cite journal</ref> ΦRmp26,<ref name = "Khanuja" >Template:Cite journal</ref> ΦRmp36,<ref name = "Khanuja" /> ΦRmp38,<ref name = "Khanuja" /> ΦRmp46,<ref name = "Khanuja" /> ΦRmp50,<ref name = "Khanuja" /> ΦRmp52,<ref name = "Khanuja" /> ΦRmp61,<ref name = "Khanuja" /> ΦRmp64,<ref name = "Khanuja" /> ΦRmp67,<ref name = "Khanuja" /> ΦRmp79,<ref name = "Khanuja" /> ΦRmp80,<ref name = "Khanuja" /> ΦRmp85,<ref name = "Khanuja" /> ΦRmp86,<ref name = "Khanuja" /> ΦRmp88,<ref name = "Khanuja" /> ΦRmp90,<ref name = "Khanuja" /> ΦRmp145,<ref name = "Khanuja" /> ΦSP,<ref name = "Lesley" /> ΦSSSS304,<ref name = "Sharma">Template:Cite journal</ref> ΦSSSS305,<ref name = "Sharma" /> ΦSSSS307,<ref name = "Sharma" /> ΦSSSS308,<ref name = "Sharma" /> and ΦT1.<ref name = "Lesley" /> Of these, ΦM5,<ref name="Johnson" /> ΦM12,<ref name="Brewer" /> Φ16-3<ref>Φ16-3 Complete Genome</ref> and ΦPBC5<ref name="PBC5" /> have been sequenced.
As of March 2020 the International Committee on Taxonomy of Viruses (ICTV) has accepted the following species in its Master Species List 2019.v1 (#35):
- Realm: Duplodnaviria, Kingdom: Heunggongvirae, Phylum: Uroviricota
- Order: Caudovirales, Family: Myoviridae, Genus: Emdodecavirus (formerly M12virus)
- Species: Sinorhizobium virus M7 (alias ΦM7)<ref name = "Finan" />
- Species: Sinorhizobium virus M12 (alias DNA phage ΦM12, type species)<ref name = "Finan" />
- Species: Sinorhizobium virus N3 (alias ΦN3)<ref name = "Lesley" />