Cycle of phage development within the bacterial cell

Summary

The present researches have been made with thePhagus lacticola (P. and O.) induced on the acid-fastMycobacterium battaglini. This is an excellent material for the study of the mycobacteriophage system because once infected with the phage it becomes transparent to electrons.Phagus lacticola, as other phages, comprises a head and a tail, both covered by a unique membrane. Inside it is possible to see a certain number of small granules, which, after the phage has been absorbed by the germ, penetrate the cell, leaving outside only an empty membrane. Once inside the cell the granules multiply, giving a moruliform body which later resembles a corn-cob. The round elements of this formation show a very small central vacuole. In time this vacuole enlarges and these elements become larger and detached, assuming an annular shape (doughnuts). Once detached, they multiply in two or four and form a rosette. The single elements detach from the rosette; each one assumes a short flagellum, which then elongates, while the annular element swells and assumes the form of a mature phage, which is freed by rupture of the cell. The phages therefore have a complex cycle of development inside the host: the various phases we have been able to see are in accordance with the cycle of other living organisms and are shown here by a series of electron micrographs.