A metabolomic approach to characterize the acid-tolerance response in Sinorhizobium meliloti

DRAGHI, WALTER OMAR; ALBICORO, FRANCISCO J.; NIEHAUS, KARSTEN; BARSCH, AIKO; PÜHLER, ALFRED; DEL PAPA, MARÍA FLORENCIA; LOZANO, MAURICIO J.; LAGARES, ANTONIO

METABOLOMICS

SPRINGER

Año: 2017 vol. 13

1573-3882

Introduction Sinorhizobium meliloti establishes a symbiosiswith Medicago species where the bacterium fixesatmospheric nitrogen for plant nutrition. To achieve a successfulsymbiosis, however, both partners need to withstandbiotic and abiotic stresses within the soil, especially that ofexcess acid, to which the Medicago-Sinorhizobium symbioticsystem is widely recognized as being highly sensitive.Objective To cope with low pH, S. meliloti can undergoan acid-tolerance response (ATR(+)) that not only enablesa better survival but also constitutes a more competitivephenotype for Medicago sativa nodulation under acidand neutral conditions. To characterize this phenotype,we employed metabolomics to investigate the biochemicalchanges operating in ATR(+) cells.Methods A gas chromatography/mass spectrometryapproach was used on S. meliloti 2011 cultures showingATR(+) and ATR(−) phenotypes. After an univariate andmultivariate statistical analysis, enzymatic activities and/orreserve carbohydrates characterizing ATR(+) phenotypeswere determined.Results Two distinctive populations were clearly definedin cultures grown in acid and neutral pH based on themetabolites present. A shift occurred in the carbon-catabolicpathways, potentially supplying NAD(P)H equivalentsfor use in other metabolic reactions and/or for maintainingintracellular-pH homeostasis. Furthermore, amongthe mechanisms related to acid resistance, the ATR(+) phenotypewas also characterized by lactate production, envelopemodification, and carbon-overflow metabolism.Conclusions Acid-challenged S. meliloti exhibited severalchanges in different metabolic pathways that, in specificinstances, could be identified and related to responsesobserved in other bacteria under various abiotic stresses.Some of the observed changes included modifications inthe pentose-phosphate pathway (PPP), the exopolysaccharidebiosynthesis, and in the myo-inositol degradationintermediates. Such modifications are part of a metabolicadaptation in the rhizobia that, as previously reported, isassociated to improved phenotypes of acid tolerance andnodulation competitiveness.