Steensma H Y, Blok J
J Gen Virol. 1979 Feb;42(2):305-14. doi: 10.1099/0022-1317-42-2-305.
Infection of Bacillus subtilis 168Wt by SF 6 resulted in a rapid reduction in the number of phages. This could be counteracted by the addition of calcium, barium or strontium ions. At the optimum concentration of 7.5 x 10(-2) M, the number of p.f.u. remained constant until lysis began. Although cultures of another host. B. subtilis 31 try- his-, at the end of the logarithmic 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 therefore attributed to the fact that at least one of the steps of the lytic cycle was calcium dependent. Adsorption of SF 6 was equally effective in media containing high or low concentrations of calcium ions. Infection experiments with phages whose DNA had been labelled radioactively revealed that, at high concentrations of calcium ions, the label remained associated with the host cells until lysis commenced. At low concentrations, however, a dissociation between phage DNA and the host was found, although adsorption took place at a normal rate. From these experiments we concluded that a high concentration of calcium ions was required for the penetration of phage DNA. Similar experiments with phages whose protein coat had been labelled showed the same results, indicating that desorption of the inactivated phages occurred. Both electron microscopy and column chromatogarphy with hydroxyapatite showed that a considerable fraction of the inactivated phages had ejected their DNA into the medium. A hypothesis explaining these results is presented.
枯草芽孢杆菌168野生型被SF 6感染后，噬菌体数量迅速减少。添加钙、钡或锶离子可抵消这种情况。在最佳浓度7.5×10⁻² M时，噬菌斑形成单位（p.f.u.）数量保持恒定，直到裂解开始。尽管另一种宿主枯草芽孢杆菌31 try⁻ his⁻在对数生长期结束时产生了一种使游离噬菌体失活的物质，但这并不是低Ca²⁺浓度感染实验中p.f.u.数量减少的主要原因。因此，p.f.u.数量的减少归因于裂解循环的至少一个步骤依赖于钙这一事实。SF 6在高钙或低钙浓度的培养基中的吸附效果相同。用放射性标记DNA的噬菌体进行的感染实验表明，在高钙浓度下，标记物在裂解开始前一直与宿主细胞结合。然而，在低浓度下，尽管吸附以正常速率发生，但发现噬菌体DNA与宿主发生了解离。从这些实验中我们得出结论，噬菌体DNA的穿透需要高浓度的钙离子。用标记了蛋白质外壳的噬菌体进行的类似实验也得到了相同的结果，表明失活的噬菌体发生了解吸附。电子显微镜和羟基磷灰石柱色谱分析均表明，相当一部分失活的噬菌体已将其DNA释放到培养基中。本文提出了一个解释这些结果的假说。
