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

DRAGHI, W.O.; DEL PAPA, M.F.; HELLWEG CH.; WATT S.; WATT T.; BARSCH A.; LOZANO, M.J.; LAGARES, A. (JR); SALAS, M.E.; LÓPEZ, J.L.; ALBICORO, F.; NILSSON, J. N.; TORRES TEJERIZO, G.A.; LUNA, M.F.; PISTORIO, M.; BOIARDI, J. L.; PUHLER, A.; WEIDNER, S.; NIEHAUS, K.; LAGARES, A.

Scientific Reports

NPG Publishing Group

Lugar: Londres; Año: 2016 vol. 6 p. 1 - 19

Abiotic stresses in general and extracellular acidity in particular disturb and limit nitrogen-fixingsymbioses between rhizobia and their host legumes. Except for valuable molecular-biological studieson different rhizobia, no consolidated models have been formulated to describe the central physiologicchanges that occur in acid-stressed bacteria. We present here an integrated analysis entailing the maincultural, metabolic, and molecular responses of the model bacterium Sinorhizobium meliloti growingunder controlled acid stress in a chemostat. A stepwise extracellular acidification of the culture mediumhad indicated that S. meliloti stopped growing at ca. pH 6.0?6.1. Under such a stress the rhizobiaincreased the O2 consumption per cell by more than 5-fold. This phenotype, together with an increase inthe transcripts for several membrane cytochromes, entails a higher aerobic-respiration rate in the acidstressed rhizobia. Multivariate analysis of global metabolome data served to unequivocally correlatespecific-metabolite profiles with the extracellular pH, showing that at low pH the pentose-phosphatepathway exhibited increases in several transcripts, enzymes, and metabolites. Further analyses shouldbe focused on the time course of the observed changes, its associated intracellular signaling, and onthe comparison with the changes that operate during the sub lethal acid-adaptive response (ATR) inrhizobia