Bacterial nitrogen fixation is an important element of the nitrogen cycle. The efficiency of this process constitutes a scientific challenge with direct implication in agronomy and plant development. The contribution of the present work is twofold. First, we present a genome scale metabolic network reconstruction for Rhizobium etli CFN42, a nitrogen fixing bacterium. The network includes 387 metabolic and transport reactions across 28 metabolic pathways. Second, an objective function is suggested to study the phenotypic properties during symbiotic nitrogen fixation. Constraint-based in silico analysis was performed and the active metabolic pathways predicted by the model were in qualitative agreement with experimental measurements. In addition, the computed consequences of knockouts in PHB(poly-hydroxybutyrate)and glycogen synthase are predicted. Their consistency with respect to nitrogen fixation are analyzed. Thus, as for other organisms, a reconstructed genome-scale for R. etli CFN42 metabolic network constitutes an important framework which allows us to compare the predictions with experiments and test hypotheses to improve nitrogen fixation. Finally, through construction and analysis of a dynamic model, we suggest that symbiosis between plant-bacteroid could be a multi steady-state phenomena.

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