SYNTHESIS OF GLYCEROPHOSPHORYLATED CYCLIC (1,2)BETA-GLUCANS IN RHIZOBIUM-MELILOTI STRAIN-1021 AFTER OSMOTIC SHOCK

The transfer of phosphoglycerol moieties from phosphatidylglycerol to the cyclic (1,2)-beta-glucans in growing cultures of Rhizobium meliloti strain 1021 was investigated using pulse-chase experiments with [H-3]glycerol and/or [C-14]glucose. No transfer occurred when cells were grown and pulse-chased in a medium containing 0.4 M NaCl. However, radiolabelled glycerophosphorylated cyclic (1,2)-beta-glucans could be detected within 30 min after transfer of these cultures to a low-osmolarity medium. Conversely, when low-osmolarity cultures were shifted to a high-osmolarity medium containing 0.4 M NaCl or 0.8 M sucrose, the transfer of phosphoglycerol substituents to the cyclic (1,2)-beta-glucans was inhibited. Further experiments revealed that the transfer of phosphoglycerol substituents to the cyclic (1,2)-beta-glucans occurs within the periplasmic compartment.