Rhizobia

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Rhizobia

 

(nodule bacteria), bacteria of the genus Rhizobium, which form small nodules on the roots of certain legumes, symbiotically fix molecular nitrogen, and produce in the process a number of physiologically active substances with beneficial effects on the legumes.

Rhizobia play an important part in enriching soils with nitrogen. The young bacteria, which measure 0.5–0.9 X 1.2–3 microns, are nonsporiferous, motile, gram-negative, and aerobic. Entering a root hair, they bring about the active division of the root cells. This leads to the appearance of a small nodule. The rhizobia grow in the nodule, turning into thickened and branched forms called bacteroids. These actively fix molecular nitrogen. Rhizobia also assimilate ammonium salts, nitrates, and amino acids. Their sources of carbon can be monosaccharides, disaccharides, certain polysaccharides, organic acids, and alcohols. On smooth culture media, rhizobia form round, colorless, transparent, mucoid colonies, which grow well at 25°C. The nodules formed by active rhizobia contain the pigment leghemoglobin, which gives them a rosy color.

Different rhizobia cause the dvelopment of nodules in specificlegumes; Rhizobium meliloti in alfalfa and melilot; Rh. leguminosarum in vetch, peas, and fodder beans; Rh. trifolii inclover, and Rh. japonicum in soy. When the nodules are destroyed the rhizobia survive in the soil as saprophytes. The seeds of legumes are infected with rhizobia in order to promote nodule formation; this is an aspect of what is known as bacterial fertilization.

A. A. IMSHENETSKII

References in periodicals archive ?
Five soil samples out of 45 that support the best plant growth were selected for isolation of Rhizobium bacteria. The root nodules of respective plants were carefully cut and subjected to surface sterilization.
Lindstrom, "Diversity of Rhizobium bacteria isolated from the root nodules of leguminous trees," International Journal of Systematic Bacteriology, vol.
Infection of plants by Rhizobium bacteria (Ti) is a multistage process.
Colonization and growth promotion of non-legumes by Rhizobium bacteria. Microbial Biosystems: New Frontiers.
Hungeria (2000) studied soybean cultivars and Brady rhizobium bacteria and stated that the interactive effect of cultivar and bacteria on the trait was significant [12].
Rhizobium bacteria are naturally occurring nitrogen-fixing bacteria.
Essex also enjoys a symbiotic relationship with beneficial soil microbes, specifically root-colonizing Rhizobium bacteria, which can take nitrogen from the atmosphere and turn it into a form plants can use for growth.
Essex also enjoys a symbiotic relationship with beneficial soil microbes-specifically, root-colonizing Rhizobium bacteria, whose ability to take nitrogen from the atmosphere and turn it into a form plants can use for growth helps naturally replenish the soil's fertility for subsequent crops of wheat and other grains.
Farmers can also replenish soil's nitrogen stores by growing legumes such as alfalfa and soybeans, which partner with Rhizobium bacteria to fix nitrogen.
Legumes like peas, beans and cloves have the ability to fix atmospheric nitrogen for their own use and for the benefit of neighboring plants via the Rhizobium bacteria. Hence, the indigenous practice of interplanting beans with corn.
There are decreases in the competition strength of inoculated Rhizobium bacteria with the native ones.