OBSERVATIONS ON THE INITIAL CYTOLOGICAL EFFECTS OF BACTERIOPHAGE INFECTION
Chromatin aggregation is the earliest cytological effect of several phage infections (e.g. P1, P2, and T7). This occurs at low multiplicities of infection if the medium contains a sufficient quantity of sodium chloride; on salt-deficient medium this aggregation no longer appears and is replaced by fragmentation. Infections with phages T2 and T5 do not normally result in the aggregation of the host chromatin, but this does occur when the multiplicity of infection is higher than three to six phages per cell and salt is present in the medium. The appearance of nuclear aggregation as the first cytological effect of infection under these circumstances adds an additional cytological stage. In the case of infection with T5 this is followed by chromatin disappearance, which is the normal first stage. Infections with T5, at high multiplicities, on salt-deficient agar cause chromatin fragmentation and no aggregation.Chromatin aggregation was again the major alteration in cell structure when T2 bacteriophage "ghosts" were adsorbed. Since injection of phage DNA and phage multiplication do not occur under these conditions, it is concluded that adsorption alone is sufficient to cause this effect.It is hypothesized that adsorption of phage alters the host cell surface so that the cell can no longer maintain an ionic equilibrium. The shift in internal ion balance is reflected in chromatin aggregation or fragmentation depending on the salt concentration of the medium.