Escherichia coli capsule bacteriophages. VIII. Fragments of bacteriophage 28-1

As described previously, a host capsule depolymerase activity is associated with the particles of Escherichia coli capsule bacteriophage 28-1. This is a large virus with a long, contractile tail terminating in a base plate with spikes. In the present work, isolated virions were exposed to a variety of dissociative reagents and conditions. They were then tested for residual infectivity and depolymerase activity, as well as inspected under an electron microscope. Very mild acid treatment (10 to 15 min at pH 4.0 and 37 C) was found to cause a specific detachment of some phage spikes, together with a moderate drop in both infectivity and depolymerase activity. Large batches of viruses were fragmented in this manner, and the detached spikes were isolated. The host capsule depolymerase activity was found to be associated with these organelles. In negatively stained preparations, the spikes exhibited a length of approximately 18 nm and a thickness of about 5 nm. By sodium dodecyl sulfate-polyacrylamide gel electrophoresis, they were found to contain polypeptides with molecular weights of 80,000 and 145, 000.