ROUNTREE, P. M. (1951). J. gen. Microbiol. 5, 673-680. The Role of Certain Electrolytes in the Adsorption of

SUMMARY: The role of electrolytes in the adsorption of the citrate-sensitive staphylococcal typing-phages and the citrate-insensitive phage K on to their propagating strains was studied in broth+ Na citrate and in distilled water+ CaCI,, MgCl,, and NaCl. Some phages when in the free state were partially inactivated by 1 yo (w/v) Na citrate. In all except two phages, K and 51, citrate inhibited adsorp-tion in broth; adsorption occurred in distilled water. Three phages, 7,42B and 42E, had a specific requirement of 50 pg. CaCl,/ml. for adsorption. With the remainder, the requirements of CaCl, varied from 5 to 400 pg./ml.; similar amounts of MgCl, acted equally well. With the citrate-sensitive phages adsorption in NaCl was variable and, where it occurred, recovery of viable phage from cells infected in NaCl was less than from cells infected in CaCl,. These phages appear to have a specific requirement of divalent cations for adsorption, suggesting that adsorption and penetration are enzymic in character. The electrolyte requirements of the citrate-insensitive phage K were relate