Sinorhizobium medicae

Sinorhizobium medicae is a species of gram-negative, nitrogen-fixing, rod-shaped bacteria. They can be free-living or symbionts of leguminous plants in root nodules. S.medicae was first isolated from root nodules on plants in the genus Medicago.[1] Some strains of S.medicae, like WSM419, are aerobic. They are chemoorganotrophic mesophiles that prefer temperatures around 28 °C. In addition to their primary genome, these organisms also have three known plasmids, sized 1,570,951 bp, 1,245,408 bp and 219,313 bp.[2]

Sinorhizobium medicae
Scientific classification
Kingdom:
Bacteria
Phylum:
Proteobacteria
Class:
Alphaproteobacteria
Order:
Rhizobiales
Family:
Rhizobiaceae
Genus:
Sinorhizobium
Species:
S. medicae
Binomial name
Sinorhizobium medicae
Rome et al. 1996

Colonies of Sinorhizobium medicae are mucoid and ring-shaped and can be viewed here.

Phylogeny/Taxonomy

The genus is sometimes referred to as Ensifer (the older term) instead of Sinorhizobium. Two major subgroups include S.medicae strain A321 and S. medicae strain WSM419. this phylogenetic tree shows relatedness to the rest of the Rhizobiaceae family based on 16s rRNA gene sequences.

Ecological role and symbiosis with legumes

This bacterium is often involved in mutualistic relationships with legumes. It performs atmospheric nitrogen fixation for the plants and in exchange it receives organic carbon through the process of rhizodeposition. Free-living bacteria become housed inside specialized root cells in root nodules, which creates anaerobic microhabitat in which efficient N-fixation can occur. This mutualism has been observed with many plant species, including Medicago polymorpha and Medicago truncatula plants from around the world.[3] The extent of the mutualism may be dependent upon soil pH, as it was thought that acidity can constrain Sinorhizobium medicae. Current thinking is that acid resistance, particularly in strain WSM419, can be transferred on plasmids.[4]

Agricultural Importance

Because S. medicae associates well with plants in the genus Medicago and increases plants growth, crop fields are commonly inoculated with the bacteria in addition to or in replacement of synthetic fertilizers.[5]

References
  1. Chen, WX; Yan, GH; Li, JL (1988). "Numerical taxonomic study of fast-growing soybean rhizobia and a proposal that Rhizobium fredii be assigned to Sinorhizobium gen. nov". International Journal of Systematic Bacteriology. 38 (4): 392–397. doi:10.1099/00207713-38-4-392.
  2. Reeve, W; Chain, P; O'Hara, G; Ardley, J; Nandesena, K; Bräu, L; Tiwari, R; Malfatti, S; Kiss, H; Lapidus, A; Copeland, A; Nolan, M; Land, M; Hauser, L; Chang, YJ; Ivanova, N; Mavromatis, K; Markowitz, V; Kyrpides, N; Gollagher, M; Yates, R; Dilworth, M; Howieson, J (2010). "Complete genome sequence of the Medicago microsymbiont Ensifer(Sinorhizobium) medicae strain WSM419". Standards in Genomic Sciences. 2 (1): 77–86. doi:10.4056/sigs.43526. PMC 3035259. PMID 21304680.
  3. Rome, S; Fernandez, MP; Brunel, B; Normand, P; Cleyet-Marel, JC (1996). "Sinorhizobium medicae sp. nov., isolated from annual Medicago spp". International Journal of Systematic Bacteriology. 46 (4): 972–980. doi:10.1099/00207713-46-4-972. PMID 8863426.
  4. "Sinorhizobium medicae WSM419". JGI Genome Portal. US Department of Energy.
  5. Shi, Ruihua. Sinorhizoibum Genome Sequencing, Annotation and Nitrogen Fixation. University of Oklahoma. ISBN 9780549576518.
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