Biological nitrogen fixation is an important aspect of nitrogen nutrition in crop production throughout the world. The process saves a huge sum of money, which otherwise would have to the pumped into agricultural productivity to consistently sustain an increasing world population. Among the various symbiotic associations, the Rhizobium - legume association is the most common in both temperate and tropical climates.The importance is not only limited to plant nutrition, but increasing environmental concerns indicate that high input of nitrogen fertilizers in agriculture may lead to many...