Effect of Calcium Ions on the Infection of Bacillus subtilis by Bacteriophage SF 6

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Abstract
Infection of B. subtilis 168 Wt by SF 6 resulted in a rapid reduction in the number of phages. This could be counteracted by the addition of Ca, Ba or Sr ions. At the optimum concentration of 7.5 .times. 10-2 M, the number of p.f.u. [plaque forming units] remained constant until lysis began. Although cultures of another host, B. subtilis 31 try- his-, at the end of the log growth phase produced a substance which inactivated free phages, this was not the major cause of the reduction in the numbers of p.f.u. during infection experiments at low Ca2+ concentrations. The diminution of the number of p.f.u. was attributed to the fact that at least 1 of the lytic cycle was Ca dependent. Adsorption of SF 6 was equally effective in media containing high or low concentrations of Ca ions. Infection experiments with phages whose DNA was labeled radioactively revealed that, at high concentrations of Ca ions, the label remained associated with the host cells until lysis commenced. At low concentrations, a dissociation between phage DNA and the host was found, although adsorption took place at a normal rate. Apparently a high concentration of Ca ions was required for the penetration of phage DNA. Similar experiments with phages whose protein coat was labeled showed the same results, indicating that desorption of the inactivated phages occurred. EM and column chromatography with hydroxyapatite showed that a considerable fraction of the inactivated phages ejected their DNA into the medium. A hypothesis explaining these results is presented.