Classical an omic approaches to the analysis of acid-stressed alfalfa nodulation rhizobia

WALTER OMAR DRAGHI; MARÍA FLORENCIA DEL PAPA; MARIANO PISTORIO; MARÍA LAURA MOLINARI; MAURICIO LOZANO; MARÍA DE LOS ANGELES GIUSTI; JOSÉ LUIS BOIARDI; STEVEN WATT; KARSTEN NIEHAUS; ALFRED PÜHLER; ANTONIO LAGARES

Universidad Austral, Pilar, Buenos Aires, Argentina

Congreso; 1st Annual Iberoamerican PROTEOMICS Congress.; 2007

Latinamerican Human Proteome Organisation (LAHUPO)

The poor tolerance of several rhizobia to the hidrogen ions is considered among the main factors thet restrict the development of de N2-fixing symbiosis in moderately acidic soils. This circumstance reinforces de necessity to better undestand the molecular basis of the rhizobial response to acidity. To advance in this direction, and to investigate te relevance of differentially expressed proteins markers, we set up N-limited continuous cultures of the model strain Snorhizobium meliloiti (Sme) 2011 at differents pHs and characterized their proteomes. In such experiments the extacellular pH was gradually dicreased 0.2-0.5 units (± 0.05) stepwise starting from a continuos culture at pH 7.4. Results showed that: strain Sme 2011 stopped growing when reaching pHs lower than 6.1 in the chemostat (this considered the pHlimit). 2D-gel electrophoresis-MALDI-TOF proteome analysis of strain 2011 sempled from the chemostat and from batch cultures at diffferent pHs allowed for the identification of several proteins associated to the growth under each pH condition. We recognized 8 and 22 differentially expressed proteins associated to the acid and to the neutral condition, respectively. Te up-regulated proteinsunder acidityincluded: Ppi and Tig (peptidyl-prolyl isomerases, one of them ribosoma-associated), SodB (superoxide dismutase), DegP1 (protease), TufA (translation factor), Mur (murein synthesis), and other proteins involved in the biosynthesis and/or transport of small molecules. Most of the acid-induced proteins were related to the support of housekeeping activities and to the recoery of protein structure/activities, denoting a clear reactive behavior of the cells against the operating stress condition. A very similar pattern of over/under expression was obseved for the differential proteome markers at the transcriptomme level, Showing a highly positive correlation between the proteome and transceiptome data under our experimental conditions. Most relevant, sever single-Tn5 mutants affected in the identiied proteome markers showed a more acid sensitive phenotype. Thus, the collected data provided experimental support to screen and compare, at a functional level, the individul contribution of acid-induced/repressed marker to the growth of Sme under acidity.