Effect of ion concentration on the rupture and survival of Azotobacter cysts.

The ability of ethylenediaminetetraacetic acid (EDTA) and dipicolinic acid (DPA) to rupture Azotobacter cysts was directly related to the molarity of the reaction mixture. Cysts were not ruptured at concentrations above 0.15 m (NaCl or phosphate). These higher salt concentrations prevented the formation of metallo:EDTA (or DPA) chelate complexes. Sudden shifts in the tonicity of NaCl or phosphate mixtures induced cyst rupture in the absence of EDTA. The effect of these mechanisms on the survival and germination of Azotobacter cysts in the soil is discussed.