Osmotic Properties of Protoplasts of Micrococcus lysodeikticus

SUMMARY: Protoplasts were released from Micrococcus lysodeikticus by the action of lysozyme in media containing sucrose, NaCl or mixtures of these. Empirical corrections by two methods were made for the effect of refractive index on the optical density of the protoplast suspensions measured at 500 mμ. With the assumption, valid for some similar systems, that the optical density of a protoplast suspension is inversely proportional to the protoplast volume, the protoplasts were shown to behave as osmometers at osmotic pressures above the threshold for lysis and to follow a van’t Hoff-Boyle law. The osmotically-inactive volume in a standard stabilizing medium containing m-sucrose + 0·05m-NaCl (osmotic pressure 37·8 atm.) was c. 76 %. Protoplasts formed in hypotonic media were more resistant to osmotic explosion than those formed at higher medium concentrations and subsequently diluted.