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

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

La Falda

Workshop; II Workshop Latinoamericano sobre PGPR; 2014

UNRC - UNQui - Univ. Antioquia

Sinorhizobium meliloti is a gram-negative proteobacterium able to establish nitrogen-fixingsymbiosis with legumes of the genera Medícogo, Melilotus, and Trígonella. This association istightly regulated. Either in the process of infection of the plant host or in free-living stage, rhizobialstrains must adapt and respond to different environmental stimuli, including those from the planthost. This leads us to investigate the role of two-component signal transduction in the regulation ofS. meliloti physiology. The cellular roles of most two-component systems (TCS) and the genes theyactivate remain unknown. We used a bioinformatics approach to identify the two-componentsystems (TCS) of S. meliloti. The available S. melilotigenome and the followíng tools were used:Simple Modular Architecture Research Tool (SMART), Pfam programs, and BLAST. By bioinformaticsanalysis, we identified the TCS consisting of a 40 sensory histidine-kinases (HK), including 8 hybridHKs and 60 response regulator. ln an effort to identify the potential function of each TCS in thebiology of S. meliloti strain zOLl, we analyzed the consequences of the disruption of the RR. 5.melilotí zOLl response regulators (RR) mutants were obtained either by TnS transposonmutagenesis (Pobigaylo et al 2006) or constructed by single cross-over method, At the moment, weobtained a collection of 35 mutants, 22of them generated by In5 transposon mutagenesis and theother 13 were achieved by single cross-over method. By this method, we were not able toinactivate an ortholog of ctrA,this gene has beenpreviously shown to be one of the key genesinvolved in the viability of some gram-negative micioorganisms. The biological effects of the 35mutations were assessed by biofilm formatíon and environmental stress. We identified TCS relatedto acid and osmotic environmental stress in S. meliloti. The characterization of the RR genesimplicated in the response to stress, their regulatíon, hierarchical role and specificity is a valuabletool for the understanding of basic aspects in the symbiosis process. This approach could contributeto the rational and efficient biotechnological improvement of inoculant rhizobia.