Nature of the salt dependence of the envelope of a Dead Sea archaebacterium, Haloferax volcanii

The external layer was released from Haloferax volcanii cells and envelopes when the divalent cation concentration was lowered in the presence of NaCl. NaCl alone could not stabilize the isolated envelopes and divalent cations were absolutely required at concentrations which depended on that of NaCl and on the temperature. NaCl and divalent cations had a cooperative or an antagonistic effect according to their relative concentrations. The envelopes were optimally stabilized by a combination of NaCl and divalent cations, which probably ensured an equilibrium between the hydrophobic bonds and the charge shielding effects involved in the structure of cell envelope (cytoplasmic membrane and external layer).