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A consolidated analysis of the physiologic and molecular responses induced under acid stress in the legume-symbiont model-soil bacterium Sinorhizobium meliloti

2016; Nature Portfolio; Volume: 6; Issue: 1 Linguagem: Inglês

10.1038/srep29278

2045-2322

Walter Omar Draghi, María Florencia Del Papa, Christoph Hellweg, Stephen A. Watt, Tony Watt, Aiko Barsch, Mauricio J. Lozano, Antonio Lagares, María Eugenia Salas, José Luis López, Francisco Javier Albicoro, Juliet F. Nilsson, Gonzalo Torres Tejerizo, María Flavia Luna, Mariano Pistorio, J. L. Boiardi, Alfred Pühler, Stefan Weidner, Karsten Niehaus, Antonio Lagares,

Plant nutrient uptake and metabolism

Abstract Abiotic stresses in general and extracellular acidity in particular disturb and limit nitrogen-fixing symbioses between rhizobia and their host legumes. Except for valuable molecular-biological studies on different rhizobia, no consolidated models have been formulated to describe the central physiologic changes that occur in acid-stressed bacteria. We present here an integrated analysis entailing the main cultural, metabolic, and molecular responses of the model bacterium Sinorhizobium meliloti growing under controlled acid stress in a chemostat. A stepwise extracellular acidification of the culture medium had indicated that S. meliloti stopped growing at ca. pH 6.0–6.1. Under such stress the rhizobia increased the O 2 consumption per cell by more than 5-fold. This phenotype, together with an increase in the transcripts for several membrane cytochromes, entails a higher aerobic-respiration rate in the acid-stressed rhizobia. Multivariate analysis of global metabolome data served to unequivocally correlate specific-metabolite profiles with the extracellular pH, showing that at low pH the pentose-phosphate pathway exhibited increases in several transcripts, enzymes, and metabolites. Further analyses should be focused on the time course of the observed changes, its associated intracellular signaling, and on the comparison with the changes that operate during the sub lethal acid-adaptive response (ATR) in rhizobia.