Magnesium Orthophosphate,a New Form of Reserve Phosphate in the Halophilic Archaeon Halobacterium salinarium

The accumulation and utilization of reserve phosphate in the extremely halophilic archaeon Halobacterium salinarium were studied. The growth of H. salinarium was found to depend on the initial concentration of inorganic phosphate (P_i) in the culture medium and its content in the inoculum. Growing cells consumed 85–95% of P_i from the medium. Unlike the reserve phosphates of many other microorganisms, which are mainly polyphosphates, the reserve phosphates of H. salinarium cells contain no more than 15% polyphosphates, the rest being magnesium orthophosphate. The excessive consumption of P_i from the medium led to a change in cell morphology and caused the death of part of the cell population. The cells that remained viable could grow in a P_i-deficient medium, utilizing about 70% of the reserve magnesium phosphate as the phosphorus source.