The role of divalent cations in the multiplication of staphylococcal bacteriophages.

The staphylococcal typing phages require divalent cations for a stage in phage growth which is probably that of penetration. When phage is adsorbed to the cell surface of sensitive cocci and a chelating agent is added, there is a short period during which the phage particle may be inactivated and its lethal effect on the coccus prevented. Cocci attacked by phages of serological group A show penetration of the phages in distilled water + CaCl,, or + MgCl, , or to a less extent + SrCl,. The phages of group B are unable to penetrate in presence of SrC1, and in some cases MgCl, is only partially active as compared with CaCl,. Ca ions appear to be required specifically a t a late stage in phage synthesis since the average yield of phage/coccus increases with increasing concentration of CaCl, ; the addition of a chelating agent towards the end of the latent period depresses the yield of phage.