Sinorhizobium meliloti (Dangeard, 1926) De Lajudie et al., 1994
Ensifer meliloti (formerly Rhizobium meliloti and Sinorhizobium meliloti)[10] are an
aerobic,
Gram-negative, and
diazotrophic species of bacteria. S. meliloti are
motile and possess a cluster of peritrichous
flagella.[11]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.[12] These techniques reduce the need for inorganic nitrogenous
fertilizers.[13]
Symbiosis
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′-methoxy
chalcone,[14]chrysoeriol,[15]cynaroside,[15]4′,7-dihydroxyflavone,[14] 6′′-O-malonylononin,[16]liquiritigenin,[14]luteolin,[17] 3′,5-dimethoxyluteolin,[15] 5-methoxyluteolin,[15]medicarpin,[16] stachydrine,[18] and
trigonelline.[18] 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.[19]
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.[20]
Genome
The S. melilotigenome contains four genes coding for flagellin. These include fliC1C2–fliC3C4.[11] 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,[21] AK83,[22] BL225C,[22] Rm41,[23] and SM11[24] with 1021 considered to be the
wild type. Indeterminate nodule symbiosis by S. meliloti is conferred by genes residing on pSymA.[25]
DNA repair
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.[26] 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.
^Rogel MA, Ormeño-Orrillo E, Martinez Romero E (April 2011). "Symbiovars in rhizobia reflect bacterial adaptation to legumes". Systematic and Applied Microbiology. 34 (2): 96–104.
doi:
10.1016/j.syapm.2010.11.015.
PMID21306854.
^León-Barrios M, Lorite MJ, Donate-Correa J, Sanjuán J (September 2009). "Ensifer meliloti bv. lancerottense establishes nitrogen-fixing symbiosis with Lotus endemic to the Canary Islands and shows distinctive symbiotic genotypes and host range". Systematic and Applied Microbiology. 32 (6): 413–20.
doi:
10.1016/j.syapm.2009.04.003.
PMID19477097.
^Villegas Mdel C, Rome S, Mauré L, Domergue O, Gardan L, Bailly X, Cleyet-Marel JC, Brunel B (November 2006). "Nitrogen-fixing sinorhizobia with Medicago laciniata constitute a novel biovar (bv. medicaginis) of S. meliloti". Systematic and Applied Microbiology. 29 (7): 526–38.
doi:
10.1016/j.syapm.2005.12.008.
PMID16413160.
^Mnasri B, Mrabet M, Laguerre G, Aouani ME, Mhamdi R (January 2007). "Salt-tolerant rhizobia isolated from a Tunisian oasis that are highly effective for symbiotic N2-fixation with Phaseolus vulgaris constitute a novel biovar (bv. mediterranense) of Sinorhizobium meliloti". Archives of Microbiology. 187 (1): 79–85.
doi:
10.1007/s00203-006-0173-x.
PMID17019605.
S2CID24133146.
^Gubry-Rangin C, Béna G, Cleyet-Marel JC, Brunel B (October 2013). "Definition and evolution of a new symbiovar, sv. rigiduloides, among Ensifer meliloti efficiently nodulating Medicago species". Systematic and Applied Microbiology. 36 (7): 490–6.
doi:
10.1016/j.syapm.2013.06.004.
PMID23871297.
^The sequence hasn't been officially announced, but is available at NCBI:
chromosome,
pSymA,
pSymB, and
pRM41a.
^Schneiker-Bekel S, Wibberg D, Bekel T, Blom J, Linke B, Neuweger H, Stiens M, Vorhölter FJ, Weidner S, Goesmann A, Pühler A, Schlüter A (August 2011). "The complete genome sequence of the dominant Sinorhizobium meliloti field isolate SM11 extends the S. meliloti pan-genome". Journal of Biotechnology. 155 (1): 20–33.
doi:
10.1016/j.jbiotec.2010.12.018.
PMID21396969.
^Humann JL, Ziemkiewicz HT, Yurgel SN, Kahn ML. Regulatory and DNA repair genes contribute to the desiccation resistance of Sinorhizobium meliloti Rm1021. Appl Environ Microbiol. 2009 Jan;75(2):446-53. doi: 10.1128/AEM.02207-08. Epub 2008 Nov 21. PMID 19028909; PMCID: PMC2620701
^
abcdeSystematic 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.
^
abSingh RB, Dhar B, Singh BD (1986). "Morphology and general characteristics of viruses active against cowpea Rhizobium CB756 and 32H1". Archives of Virology. 64 (1): 17–24.
doi:
10.1002/jobm.3620270309.
PMID7377972.
S2CID84732610.
^
abcdefgKrsmanovi-Simic D, Werquin M (1977). "Etude des bactériophages de Rhizobium meliloti" [Study of bacteriophages of Rhizobium meliloti]. Comptes Rendus de l'Académie des Sciences, Série D (in French). 284: 1851–1854. and Krsmanovi-Simic D, Werquin M (1973). "Etude des bactériophages de Rhizobium meliloti" [Study of bacteriophages of Rhizobium meliloti]. Comptes Rendus de l'Académie des Sciences, Série D (in French). 276 (19): 2745–8.
PMID4198859.
^
abcdefghijklmnopqrstuKowalski M (1967). "Transduction in Rhizobium meliloti". Acta Microbiologica Polonica. 16 (1): 7–11.
doi:
10.1007/BF02661838.
PMID4166074.
S2CID10908418. Note that this article was reprinted in Plant and Soil (1971) 35 (1): 63—66, which is where the URL and doi direct to.
^
abcdeCorral E, Montoya E, Olivares J (1978). "Sensitivity to phages in Rhizobium meliloti as a plasmid consequence". Microbios Letters. 5: 77–80.
^
abcdeKowalski M, Małek W, Czopska-Dolecka J, Szlachetka M (2004). "The effect of rhizobiophages on Sinorhizobium meliloti–Medicago sativa symbiosis". Biology and Fertility of Soils. 39 (4): 292–294.
doi:
10.1007/s00374-004-0721-y.
S2CID26352194.
^Wdowiak S, Małek W, Grzadka M (February 2000). "Morphology and general characteristics of phages specific for Astragalus cicer rhizobia". Current Microbiology. 40 (2): 110–3.
doi:
10.1007/s002849910021.
PMID10594224.
S2CID5181655.
^Małek W (1990). "Properties of the transducing phage M1 of Rhizobium meliloti". Journal of Basic Microbiology. 30 (1): 43–50.
doi:
10.1002/jobm.3620300114.
S2CID86226063.
^
abcdeWerquin M, Ackermann HW, Levesque RC (1989). "Characteristics and comparative study of five Rhizobium meliloti bacteriophages". Current Microbiol. 18 (5): 307–311.
doi:
10.1007/BF01575946.
S2CID11937563.
^
abThis phage has never been formally reported in the scientific literature. However, the full genomic sequence has been uploaded to NCBI, available
here.
^Novikova NI, Bazenova OV, Simarov BV (1987). "Phage sensitivity of natural and mutant strains of alfalfa nodule bacteria differing by cultural and symbiotic properties. (Summary in English)". Agric. Biol. 2: 35–39.
^
abcdefghijklmnopKhanuja SP, Kumar S (1989). "Symbiotic and galactose utilization properties of phage RMP64-resistant mutants affecting three complementation groups in Rhizobium meliloti". Journal of Genetics. 68 (2): 93–108.
doi:
10.1007/BF02927852.
S2CID25258531.
^
abcdSharma RS, Mishra V, Mohmmed A, Babu CR (April 2008). "Phage specificity and lipopolysaccarides of stem- and root-nodulating bacteria (Azorhizobium caulinodans, Sinorhizobium spp., and Rhizobium spp.) of Sesbania spp". Archives of Microbiology. 189 (4): 411–8.
doi:
10.1007/s00203-007-0322-x.
PMID17989956.
S2CID5746480.
Chi F, Yang P, Han F, Jing Y, Shen S (May 2010). "Proteomic analysis of rice seedlings infected by Sinorhizobium meliloti 1021". Proteomics. 10 (9): 1861–74.
doi:
10.1002/pmic.200900694.
PMID20213677.
S2CID22652087.