IONIC STRESS AND OSMOTIC-PRESSURE INDUCE DIFFERENT ALTERATIONS IN THELIPOPOLYSACCHARIDE OF A RHIZOBIUM-MELILOTI STRAIN

A halotolerant strain of Rhizobium meliloti was isolated from nodules of a Melilotus plant growing in a salt marsh in Donana National Park ( southwest Spain), This strain, EFB1, is able to grow at NaCl concentra tions of up to 500 mM, and no effect on growth is produced by 300 mM N aCl. EFB1 showed alterations on its lipopolysaccharide (LPS) structure that can be related to salt stress: (i) silver-stained electrophoreti c profiles showed a different mobility that was dependent on ionic str ess but not on osmotic pressure, and (ii) a monoclonal antibody, JIM 4 0, recognized changes in LPS that were dependent on osmotic stress. Bo th modifications on LPS may form part of the adaptive mechanism of thi s bacterium fors aline environments.