Role of divalent cations in the subunit associations of complex flagella from Rhizobium meliloti.

Rhizobium meliloti, a symbiotic, nitrogen-fixing soil bacterium with complex flagella, as well as other members of the family Rhizobiaceae, rapidly lost motility when suspended in buffers lacking divalent cations but retained good motility in buffers containing calcium, magnesium, barium, or strontium. Loss of motility was associated with loss of flagella from the cells. Analysis of flagella by sedimentation, gel electrophoresis, and electron microscopy revealed that removal of divalent cations from the complex flagella of R. meliloti resulted in extensive dissociation of the flagellar filaments into low-molecular-weight subunits. Accordingly, divalent cations such as calcium and magnesium that are normally present at high concentrations in the soil solution may be crucial to the assembly and rigidity of complex flagella.