OSMOREGULATION IN RHIZOBIUM-MELILOTI - MECHANISM AND CONTROL BY OTHERENVIRONMENTAL SIGNALS

Bacteria commonly adapt to increases in the osmolarity of the environm ent by the intracellular accumulation of small organic solutes (osmoly tes) that function by restoring turgor. We have investigated the mecha nism of osmotic regulation in Rhizobium meliloti, the root nodule symb iont of alfalfa. As a soil microbe, this organism is subjected to vari able osmolarity and a number of other environmental conditions to whic h it must respond appropriately. Natural abundance C-13 nuclear magnet ic resonance spectroscopy was used to identify the osmolytes accumulat ed by osmotically stressed R. meliloti. The complement of osmolytes an d their concentrations were found to depend on the level of osmotic st ress, growth phase of the culture, carbon source, and the presence of osmolytes in the growth medium. The osmolytes accumulated by 22 differ ent bacterial strains are presented and compared to those of R. melilo ti 102F34. (C) 1994 Wiley-Liss, Inc.