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Leghemoglobin is an oxygen-carrying phytoglobin found in the nitrogen-fixing root nodules of leguminous plants. It is produced by these plants in response to the roots being colonized by nitrogen-fixing bacteria, termed rhizobia, as part of the symbiotic interaction between plant and bacterium: roots not colonized by Rhizobium do not synthesise leghemoglobin. Leghemoglobin has close chemical and structural similarities to hemoglobin, and, like hemoglobin, is red in colour. It was originally thought that the heme prosthetic group for plant leghemoglobin was provided by the bacterial symbiont within symbiotic root nodules. However, subsequent work shows that the plant host strongly expresses heme biosynthesis genes within nodules, and that activation of those genes correlates with leghemoglobin gene expression in developing nodules.
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.
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.
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.
Bradyrhizobium elkanii is a species of legume-root nodulating, microsymbiotic nitrogen-fixing bacterium originally identified as DNA homology group II strains of B. japonicum . In 1988, it was discovered that only DNA homology group II strains caused a destructive bleaching of leaves, termed scientifically "microsymbiont-induced foliar chlorosis", which was widespread in soybean production fields of the southern United States . Whole cell fatty acid content together with antibiotic resistance profiles were major phenotypic differences that helped establish DNA homology group II strains as a new species, Bradyrhizobium elkanii .
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.
Bradyrhizobium arachidis is a species of legume-root nodulating, microsymbiotic nitrogen-fixing bacterium. It was first isolated from Arachis hypogaea root nodules in China. Its type strain is CCBAU 051107T.
Bradyrhizobium liaoningense is a species of legume-root nodulating, microsymbiotic nitrogen-fixing bacterium. It was first isolated from Glycine soja and Glycine max root nodules in China. Its type strain is strain 2281.
Bradyrhizobium canariense is a species of legume-root nodulating, endosymbiont nitrogen-fixing bacterium. It is acid-tolerant and nodulates endemic genistoid legumes from the Canary Islands. The type strain is BTA-1T.
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).
Bradyrhizobium iriomotense is a species of legume-root nodulating, endosymbiont nitrogen-fixing bacterium, first isolated from Entada koshunensis. The type strain is EK05T.
Bradyrhizobium betae is a species of legume-root nodulating, microsymbiotic nitrogen-fixing bacterium first isolated from the roots of Beta vulgaris, hence its name. It is slow-growing an endophytic. The type strain is PL7HG1T.
Bradyrhizobium daqingense is a bacterium from the genus Bradyrhizobium.
Bradyrhizobium huanghuaihaiense is a bacterium from the genus of Bradyrhizobium.
Bradyrhizobium stylosanthis is a nitrogen-fixing bacterium from the genus Bradyrhizobium which has been isolated from the nodules of the plant Stylosanthes guianensis.
Bradyrhizobium kavangense is a nitrogen-fixing bacterium from the genus Bradyrhizobium which has been isolated from the nodules of the cowpea Vigna unguiculata in the Kavango region in Namibia.
Bradyrhizobium subterraneum is a nitrogen-fixing bacterium from the genus of Bradyrhizobium which has been isolated from the effective nodules of the peanut Arachis hypogaea.
Bradyrhizobium tropiciagri is a nitrogen-fixing bacterium from the genus of Bradyrhizobium.
Bradyrhizobium viridifuturi is a nitrogen-fixing bacterium from the genus of Bradyrhizobium.
A symbiosome is a specialised compartment in a host cell that houses an endosymbiont in a symbiotic relationship.
References
- 1 2 Parte, A.C. "Bradyrhizobium". LPSN .
- ↑ "Bradyrhizobium ottawaense Taxon Passport - StrainInfo". www.straininfo.net.
- ↑ "Bradyrhizobium ottawaense". www.uniprot.org.
- ↑ Yu, X; Cloutier, S; Tambong, JT; Bromfield, ES (September 2014). "Bradyrhizobium ottawaense sp. nov., a symbiotic nitrogen fixing bacterium from root nodules of soybeans in Canada". International Journal of Systematic and Evolutionary Microbiology. 64 (Pt 9): 3202–7. doi:10.1099/ijs.0.065540-0. PMC 4156109 . PMID 24969302.