Proteome analysis, acid tolerance and acid-adaptative response of Sinorhizobium meliloti (Sme) 2011 growing in continuous and in batch culture

DRAGHI, W, DEL PAPA, MF, PISTORIO, M, LOZANO, M, BOIARDI, JL, WATT, S, NIEHAUS, K, PUHLER, A Y LAGARES, A.

Merida, Mexico

Congreso; XII International Congress on Molecular Plant-Microbe Interactions; 2005

The poor tolerance of Sme to hydrogen ions is considered a main restrictive factor for the development of symbioses with Medicago spp. in acidic soils. This circumstance and the potential to extend current areas cultivated with alfalfa and other Medicago, both reinforce the necessity to understand the Sme response to acidity as well as its rational manipulation against the stressing acid challenge.In addition to the acid tolerance defined in terms of the lower pH value at which cells can support growing when diluted from a neutral batch culture, Sme like other bacteria expresses an acid-adaptive tolerance response (ATR) when grown under moderate acidity in batch cultures. To characterize the physiology and biochemistry of the Sme response to acidity, we set up and studied both batch cultures and N-limited continuous cultures of the model strain Sme 2011 at different pHs in minimal medium. Growth parameters and proteome variations were investigated to search for acid-associated protein markers. In the experiments under continuous cultivation the extracellular pH was gradually decreased 0.2-0.5 units (± 0.05) stepwise starting from a steady state culture at pH 7.0. Results showed that: Sme 2011 stopped growing when the pHs was lower than 6.1 (thus considered the pHlimit). Though at pH 6.1 a three-fold increased in the production of EPS was observed, cells sampled from the continuous cultures established at pH 7.0 and 6.1 did not display any significant difference in their decimal rate of death when suddenly exposed to pH 4.0. No link between EPS production and acid tolerance could be established. The result also indicated that growth of Sme at near its pHlimit in the chemostat was not sufficient to trigger an ATR. 2D-GE-MALDI-TOF proteome analysis of Sme 2011 sampled from both the chemostat and the batch cultures (ATR + and ATR - cells) at different pH allowed for the identification of different molecular markers associated to each growth condition. The collected data provide the basis to screen and compare the functional contribution of several acid-induced (and/or ATR-associated) markers to the free-living of Sme under moderate acidity.