Chapter 9 Genetic Construction of Stable Rhizobial Genotypes for Improved Symbiotic Nitrogen Fixation Dharmesh Harwani, Jyotsna Begani, and Jyoti Lakhani 9.1 Genetic Approaches for Improved Symbiotic Nitrogen Fixation Plant symbioses with nitrogen-fixing rhizobia have great ecological and agricul- tural importance as the source of available nitrogen. The main advantage of bio- logical nitrogen fixation (BNF) is the increase in yield potentials without the use of chemical nitrogen fertilizers and with the consequential decrease in pollution (Freiberg et al. 1997; Stephens and Rask 2000; Vance 2001). The symbiosis of plants with rhizobia is a promising model for genetic manipulations to improve the efficiency of symbiotic nitrogen fixation as it is well studied at morphological, physiological, molecular, and genetic levels. A significant amount of practical and fundamental knowledge on the biology of the rhizobia has been gathered over the years. However, due to the difficulty of examining particular bacterial genotype in the background of huge numbers of heterogeneous microbiota, most studies on the molecular ecology of rhizobia have been conceded predominantly in the last decade. The study of the establishment of rhizobial genotype introduced into natural soils, their rhizospheric colonization, nodular occupancy, and putative transformation of genetic traits all necessitate the use of appropriately tagged stable strains for their unequivocal recognition in a biologically diverse niche. During symbiosis, explicit sets of both bacteria and plant genes are expressed, establishing the basis for the differentiation process. Nitrogen is fixed by rhizobia inside the root nodules that develop and function due to the complex genetic communications between symbiotic partners. Reduction of nitrogen into ammoniac form is D. Harwani (*) • J. Begani Department of Microbiology, Maharaja Ganga Singh University, Bikaner, India e-mail: dharmesh@mgsubikaner.ac.in J. Lakhani Department of Computer Science, Maharaja Ganga Singh University, Bikaner, India © Springer International Publishing AG 2017 A.P. Hansen et al. (eds.), Rhizobium Biology and Biotechnology, Soil Biology 50, DOI 10.1007/978-3-319-64982-5_9 165