Autoaggregation and biofilm formation in Sinorhizobium meliloti are affected by NaCl.

SORROCHE, F., NIEVAS, F., ZORREGUIETA A., GIORDANO W.

Rosario

Congreso; V Congreso Argentino de Microbiología General; 2008

SAMIGE

Sinorhizobium (Ensifer) meliloti is a Gram negative soil bacteria which symbiotically associates with alfalfa roots. In resting conditions, bacterial suspensions of the S. meliloti wild type strain Rm2011 were able to autoaggregate, as a result of the adhesion among the bacteria. These cell-cell interactions were estimated with a quantitative autoaggregation assay. We found that autoaggregation was similar in bacteria grown until midexponential or stationary phases. Autoaggregation in Rm2011 exoY, a mutant strain unable to produce the exopolysaccharide succinoglycan (EPSI), was similar to the wild type strain, suggesting that succinoglycan may not be involved in the establishment of cell-cell interactions. The medium composition strongly affected autoaggregation and biofilm formation. The addition of NaCl (300 mM) to the medium caused a significant inhibition of autoaggregation in both strains. When cultured in Y manitol minimal media, both strains were able to form robust biofilms on polystyrene microtiter plates. The presence of NaCl notably altered the partition of bacterial populations into the planktonic and biofilm phases: low salt concentrations favored the formation of the biofilm phase, whereas an almost exclusive planktonic growth was observed in high salt concentrations (300 mM), in the wild type and mutant strains. Taken together, these observations suggest that NaCl-mediated inhibition of cell-cell interactions, may partly explain the reduced biofilm formation ability under high saline concentrations. On the other hand, succinoglycan may not be relevant for in vitro cell-cell interactions and biofilm formation. Supported by SECyT-UNRC, ANPCyT-PICT and CONICET.