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Abstract

fd and fr adsorb to male strains of E. coli and infect female cells, after the fd-DNA (or the fr-RNA 15) have been deproteinized by phenol and after the cells have been converted to the form of spheroplasts. fd is very heat resistant, highly antigenic and poorly adsorbing. The latency period of intracellular multiplication is 10 min (in Tryptone broth at 37 °C). The most unusual property seems to be that fd is the only phage on record which is liberated by the host cell without destruction of the host cell. The evidence for this is threefold: 1. in infected cultures phage is liberated at the rate of about 300 phage particles per bacterium per cell generation, and the growth rate of these cultures is indistinguishable from that of controls. 2. In such cultures no significant amounts of bacterial enzyme are liberated. 3. In single burst experiments it appears that more than 60% of the individual cells have liberated around 450 phage particles after about 20 min. and later produce bacterial growth as shown by turbidity. Non-lytic infection gives rise to an unstable carrier state. The phage is lost from the cells if superinfection is prevented by the addition of fd-antiserum. Lytic mutants of fd have been recorded. fr in its properties is similar to f2 and the other RNA phages and seems to be liberated by bacteriolysis, fr, due to the chemical nature of its nucleobases, is highly sensitive to hydroxylamine in slightly alkaline solution. Infection with fr in rare cases is non-lytic and leads to an unstable carrier state.