Rhizobia are able to convert dinitrogen into biologically available forms of nitrogen through their symbiotic association with leguminous plants. This results in plant growth promotion, and also in conferring host resistance to different types of stress. These bacteria can interact with other organisms and survive in a wide range of environments, such as soil, rhizosphere, and inside roots. As most of these processes are molecularly mediated, the aim of this research was to identify and quantify the exo-metabolites produced by Rhizobium etli CFN42, Rhizobium leucaenae CFN299, Rhizobium tropici CIAT899, Rhizobium phaseoli Ch24-10, and Sinorhizobium americanum CFNEI156, by nuclear magnetic resonance (NMR). Bacteria were grown in free-living cultures using minimal medium containing sucrose and glutamate. Interestingly, we found that even when these bacteria belong to the same family (Rhizobiaceae) and all form nitrogen-fixing nodules on Phaseolus vulgaris roots, they exhibited different patterns and concentrations of chemical species produced by them.
Keywords: exo-metabolomics; nitrogen fixation; nuclear magnetic resonance; rhizobia.