Evaluation of two-component systems role in saline stress response in Sinorhizobium meliloti

ALBICORO F. J.; MARTINI M. C.; NILSSON J.; SALAS M. E.; LÓPEZ J. L.; LOZANO M. J.; TORRES TEJERIZO G. A.; BECKER A.; LAGARES A.; DEL PAPA M. F.

La Falda, Córdoba

Workshop; II Workshop Latinoamericano sobre PGPR, septiembre 2014, La Falda, Cordoba, Argentina; 2014

Workshop Latinoamericano sobre PGPR

IntroductionSinorhizobium meliloti is capable of establishing a symbiotic relationship with legume roots where nitrogen fixation takes place leading to an improved plant development. This organism needs to overcome different stress conditions like high-osmolarity environments. The response of the cells is a fundamental biological question. As most bacterial species, the so-called two-component systems (TCS) are part of the complex and diverse mechanisms involved in such responses. A better understanding of osmoregulation might help in genetic strain modification, providing a powerful tool for improvements in rhizobial nodulation, nitrogen fixation and crops yield.ObjectiveThe aim of this work was to study the role of TCSs involved in high salinity response in Sinorhizobium meliloti.Materials and methodsS. meliloti 2011 response regulator (RR) mutants were obtained either by a Tn5 transposon mutagenesis or were generated by single cross-over method. For growing tests, strains were grown in SG minimal medium under normal or high salinity conditions. OD600 was continuously monitored using an ELISA microplate reader. Results and conclusionIn order to study the role of TCSs in salinity tolerance in S. meliloti, a collection of response regulators mutants was obtained. Growing rates were determined for each RR mutant as well as for the parental strain either in GS medium (normal conditions) or GS medium supplemented with 0,5M NaCl (high salt condition). Continuous measurement of OD600 over time allowed us to determine which mutants exhibited a differential growth under stress conditions. Mutants showing a differential growth rate were chosen as candidates to study whether the corresponding RR is directly or indirectly implicated in salinity stress response. This analysis enabled us to select 7 mutants that showed a reduced growth rate in the stress condition for further analysis. Among them, the cpdR mutant showed to be unable to grow in high osmolarity condition. Although this gene has been described as crucial for cell differentiation into bacteroids and co-ordination of cell cycle events, nothing was reported yet about its contribution to high salinity response/tolerance.