SUMMARY

Phage ST-I and a host range mutant, ST-I h, the only members of the q~XI74 class of bacteriophage capable of growth on male strains of Escherichia coli, were characterized with respect o their growth requirements and physical properties. These phage were found to be separable on the basis of host range and antigenic properties but not by density or morphology. Phage ST- I showed astrict requirement for the presence of divalent cations in order for growth to occur. This requirement was shown to be at the attachment stage in the infection process. Maximal adsorp-tion kinetics occurred in the presence of o-oi6 M-CaC12 and both ST-I and ST-I h showed a greater response to divalent cations than did ~XI74. The interaction f these phage with isolated bacterial cell walls showed that the adsorption site involved the lipid layers but not he muramic acid portion of the cell wall. The growth of phage ST-I on the mutant bacterial strain w-3IIO/I revealed a strict requirement for the presence of calcium at a period after attachment