Systematic inactivation and phenotypic characterization of two-component signal transduction systems of Sinorhizobium meliloti

ALBICORO F. J.; DRAGHI, W. O.; SALAS M. E.; MARTINI M. C.; ÁLVAREZ F.; TORRES TEJERIZO G. A.; PISTORIO M.; LAGARES A.; BECKER 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

Sinorhizobium meliloti is a gram-negative proteobacterium able to establish nitrogen-fixing symbiosis with legumes of the genera Medicago, Melilotus, and Trigonella. This association is tightly regulated. Either in the process of infection of the plant host or in free-living stage, rhizobial strains must adapt and respond to different environmental stimuli, including those from the plant host. This leads us to investigate the role of two-component signal transduction in the regulation of S. meliloti physiology. The cellular roles of most two-component systems (TCS) and the genes they activate remain unknown. We used a bioinformatics approach to identify the two-component systems (TCS) of S. meliloti. The available S. melilotigenome and the follow ing tools were used: Simple Modular Architecture Research Tool (SMART), Pfam programs, and BLAST. By bioinformatics analysis, we identified the TCS consisting of a 40 sensory histidine-kinases (HK), including 8 hybrid HKs and 60 response regulator. ln an effort to identify the potential function of each TCS in the biology of S. meliloti strain 2011, we analyzed the consequences of the disruption of the RR. S. melilot i 2011 response regulators (RR) mutants were obtained either by TnS transposon mutagenesis (Pobigaylo et al 2006) or constructed by single cross-over method, At the moment, we obtained a collection of 35 mutants, 22 of them generated by Tn5 transposon mutagenesis and the other 13 were achieved by single cross-over method. By this method, we were not able to inactivate an ortholog of ctrA,this gene has beenpreviously shown to be one of the key genes involved in the viability of some gram-negative microorganisms. The biological effects of the 35 mutations were assessed by biofilm formation and environmental stress. We identified TCS related to acid and osmotic environmental stress in S. meliloti. The characterization of the RR genes implicated in the response to stress, their regulat ion, hierarchical role and specificity is a valuable tool for the understanding of basic aspects in the symbiosis process. This approach could contribute to the rational and efficient biotechnological improvement of inoculant rhizobia.