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

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

METABOLOMICS

SPRINGER

Lugar: Berlin; Año: 2017 vol. 13

1573-3882

IntroductionSinorhizobium meliloti establishes a symbiosis with Medicago species where the bacterium fixes atmospheric nitrogen for plant nutrition. To achieve a successful symbiosis, however, both partners need to withstand biotic and abiotic stresses within the soil, especially that of excess acid, to which the Medicago-Sinorhizobium symbiotic system is widely recognized as being highly sensitive.ObjectiveTo cope with low pH, S. meliloti can undergo an acid-tolerance response (ATR+) that not only enables a better survival but also constitutes a more competitive phenotype for Medicago sativa nodulation under acid and neutral conditions. To characterize this phenotype, we employed metabolomics to investigate the biochemical changes operating in ATR+ cells.MethodsA gas chromatography/mass spectrometry approach was used on S. meliloti 2011 cultures showing ATR(+) and ATR(-) phenotypes. After an univariate and multivariate statistical analysis, enzymatic activities and/or reserve carbohydrates characterizing ATR(+) phenotypes were determined. ResultsTwo distinctive populations were clearly defined in cultures grown in acid and neutral soils based on the metabolites present. A shift occurred in the carbon-catabolic pathways, potentially supplying NAD(P)H equivalents for use in other metabolic reactions and/or for maintaining intracellular-pH homeostasis. Furthermore, among the mechanisms related to acid resistance, the ATR+ phenotype was also characterized by ammonia production, envelope modification, and carbon-overflow metabolism.ConclusionsAcid-challenged S. meliloti exhibited several changes in different metabolic pathways that, in specific instances, could be identified and related to responses observed in other bacteria under various abiotic stresses. We were interested in characterizing the impact of these mechanisms on the acid-tolerance response to obtain a deeper understanding of the physiology of the resistant and competitive phenotypes expressed upon confrontation with acid stress.