Rhizobia legumes’ roots and stems, to fix nitrogen

Rhizobiaare gram negative and non-pathogenic soil bacteria (Saha and Haque, 2005). Thename rhizobia firstly coined by Frank in 1889, as they form nodules on root andstem of leguminous plants (Jordan, 1984). Rhizobia are either acid or alkaliproducing and do not tolerate high temperature as well as high salt concentration(Adhikari et al., 2012). There arenumerous of rhizobial species in the soil and every species has individualinterest to its host plant. There are more than 98 species of rhizobiabelonging to 14 genera of ? and ? proteobacteria, make symbiosis with legumehost (Berrada andFikri-Benbrahim, 2014).

They have a large symbiosis island of about 860 kb intotal size that has been split into three fragments and distributed intodifferent location in genome (Kaneko etal., 2011). In general, rhizobia have the symbiotic plasmid for symbiotic nitrogenfixation genes (MacLean et al., 2007).

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Nitrogenbadly needed  element for all plantsbecause it is directly involved in the photosynthesis process of plants (Kumar et al., 2004). Leguminous plants have asymbiotic relationship with rhizobia which fix nitrogen and enrich nutritionalvalue of plants (Payakapong et al.

,2006).      Soybea(Glycine max L.) n is the world’s foremost oilseed, being used for the human being and othersand which deserved seventh among world crops by tonnage harvested (Ross-Ibarra et al., 2007). It contains unsaturatedfatty acids, minerals like Ca and P including vitamin A, B, D and differentnutritional needs. The soybean seeds contain about 40-45% protein, 18-20%edible oil, hence it is referred as “the protein hope of future” aswell as “the miracle golden bean” (Rahman, 1982).  Plants cannot fix nitrogen on their own alone but it isessential to make nutrients, amino acids and proteins (Goormachtiget al., 2014).

Through a symbiotic relationship rhizobia form nodules on legumes’ roots and stems, to fixnitrogen into a usable form. The process of this N-fixation was discovered bythe Dutch microbiologist Martinus Beijerinck. Rhizobia fix atmospheric nitrogenor dinitrogen (N2) into nitrogenous compounds, for instance, NH3,NH4+, which are then incorporated into amino acids andutilized by the plants (Djordjevic etal., 2015; McNeilland Unkovich, 2007).


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