A CYTOLOGICAL STUDY OF THE LYSOGENIZATION OFSHIGELLA DYSENTERIAEWITH P1 AND P2 BACTERIOPHAGES

NUCLEIC ACID SYNTHESIS BY A LYSOGENIC STRAIN OF ESCHERICHIA COLI INFECTED WITH ANrII MUTANT OF COLIPHAGE T2

Mutants of phage T2, of the group called rII mutants, are known to lack the parent phage's ability to form plaques on strains of Escherichia coli lysogenic for phage λ That they are capable of initiating desoxyribonucleic acid synthesis in the infected lysogenic host cells but are incapable of maintaining it has been shown by the present study using T2r7and -E. coli C112 (λs). In contrast with the superficially similar behavior shown by some other phages (e.g. λv1h), ultraviolet irradiation and consequent induction of the lysogenic culture do not release the prophage-linked inhibition of T2r7DNA synthesis. Net ribose-nucleic acid synthesis is stopped in all cultures on infection with T2r7.

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.