%0 Journal Article %A Anderson, E. S. %A Fraser, Anthea %T The Statistical Distribution of Phenotypically Modifiable Particles and Host-ranĒµe Mutants in Populations of Vi-phage II %D 1956 %J Microbiology, %V 15 %N 1 %P 225-239 %@ 1465-2080 %R https://doi.org/10.1099/00221287-15-1-225 %I Microbiology Society, %X SUMMARY: The distribution of adapted particles of Vi-phage II has been examined. Fluctuation tests in which phage A was grown for a single cycle in type A of Salmonella typhi showed that phage E1 particles conformed to a Poisson distribution in a series of small samples and cannot, therefore, be spontaneous mutants of phage A. Particles of phage D1, on the other hand, showed a clonal distribution in a similar series of samples and are thus spontaneous host-range mutants of phage A. Phage E1 reverted to phage A during a single cycle of growth in type A organisms, which confirms that phage E1 is a phenotypic modification of phage A. In contrast, phage D1 was unaltered by a single cycle of propagation in type A organisms and its mutant nature is thus verified. Phage 29 has also been shown to be a host-range mutant of Vi-phage II. The adsorption of phage A to type E1 is lethal to the bacteria, of which only a small proportion support phage growth. The general applicability of these findings to the numerous adaptations of Vi-phage II is discussed. %U https://www.microbiologyresearch.org/content/journal/micro/10.1099/00221287-15-1-225