Classification of bacterial viruses: characteristics of the T5 species and of the T2, C16 species.

Criteria for the classification of bacterial viruses were proposed by Burnet (1933), including particle size, serological relationship, and certain physiological characteristics. These criteria were applied to the definition of 12 serological groups of coli-dysentery phages. This taxonomic scheme was an important advance since it embodied the concept of phylogenetic relationships among the bacteriophages. The application of these and other criteria to the classification of the seven phages of the T series into four serological groups has been described by Delbruick (1946). Recently an additional criterion has been suggested for defining the species category (Adams, 1952) based on the outcome of the simultaneous mixed infection of a common host cell with particles of two virus strains. If the result is mutual exclusion in which the progeny of one or the other infecting virus strain but not of both is released, it was suggested that the viruses be placed in different species. If the result is a mixed progeny of both infecting virus strains together with new types resulting from recombination of parental genetic characteristics, the infecting virus strains should be considered varieties of the same species. The present paper is concerned with the application of these taxonomic criteria to three virus strains that are serologically related to colidysentery phage T5, and to phage C16 which is serologically related to the T2, T4, T6 serological group. The properties that are characteristic of the proposed T5 species are compared with those of the proposed T2, C16 species. The latter species is homologous with serological group 11 of Burnet (1933).