The structural development of a bacterial virus

Abstract

Bacteriophage precursors have been studied by breaking open infected bacterial cells and examining the intracellular material under the electron microscope. Bacterial breakage was accomplished by means of explosive decompression, a technique which will break both infected and uninfected bacteria but will not affect free virus particles. All electron microscopy was done using the spray drop method for counting the number of each type of particle found.Studies were made at uninfected bacteria in order to establish controls. Several of the structures previously reported as virus precursors were found in these controls. Samples of infected cultures were broken at frequent intervals during the latent period and the material liberated was examined under the microscope. During the first half of the latent period no structures could be seen which were not also seen in uninfected controls. About three minutes before the first appearance of intracellular phage a particle was seen which is roughly the size of a phage head and which, when dried on the microscope screen looks like a twisted fiber. These particles, which have been called "doughnuts" increase in number, initially at the same rate as the complete phage particles. However, before the end of the normal latent period their number reaches a maximum at about 35 per bacterium and then decreases as the "doughnuts" are converted into complete phage. When the "doughnuts" and phage are at about equal number intermediate particles are seen which appear to be "doughnuts" with a phage tail attached.