No abstract

A glycanase activity, catalyzing the depolymerization of host capsular polysaccharide, is associated with Escherichia coli capsule bacteriophage no. 29, a small virus with an isometric head, carrying a base plate with a set of spikes. The bacteriophage particles were disrupted by mild acid treatment (5 to 8 min at pH 3.5 and 37 C), and the enzymatically active fragments were isolated and subjected to sodium dodecyl sulfate-gel electrophoresis as well as to electron microscopy. Of the at least nine different polypeptide chains found in the complete virion, three (of 57,000 ± 3,000, 29,500 + 2,000, and 13,500 + 1,000 daltons) were detected in detached base plates. They had the appearance of six-pointed stars of about 14 nm in outer diameter, with a central hole or prop, carrying six (or, possibly, a multiple thereof) spikes. Two sizes of polypeptide chains (57,000 and 29,500) were found in pure spikes, cylindrical particles of about 14.5 to 15 nm in length and 5 nm in diameter, and one (57,000) instill capsule depolymerizingspike subunits of roughly 5 nm in diameter. Phage 29 spike preparations, homogeneous in analytical ultracentrifugation and immunoelectrophoresis, were found to have a molecular weight of' 245,000, as determined from the sedimentation equilibrium, and to contain equimolar amounts of the two polypeptides, probably three copies of each per organelle. The amino acid analysis of the isolated spikes revealed that aspartic acid, alanine, serine, and glycine are their dominant constituents; no amino sugars or other carbohydrates were detected in the preparations.

The Escherichia coli capsule bacteriophages (K phages) described herein are specific for certain capsular strains of E. coli, all of them test strains for different E. coli K antigens. The phages are not adsorbed to the acapsular mutants of their host organisms nor to similar strains with serologically and chemically different capsular polysaccharides. Thirteen E. coil (and one Klebsiella) K phages were visualized in the electron microscope. Most viruses are similar to P22 and thus belong to Bradley group C; however, one each of group A (long, contractile tail) and group B (long, noncontractile tail) was also found. All K phages were seen to carry spikes but no tail fibers were detected. These results suggest that the structures responsible for the recognition of the thick (about 400 nm or more) capsular polysaccharide gels are located in these spikes.

The free host capsule depolymerase, induced by Escherichia coli capsule bacteriophage no. 29, and causing the formation of haloes around its plaques, has been purified to homogeneity. As judged from the following facts, this "enzyme" consists of free phage 29 spikes. (i) Detached phage organelles and depolymerase 29 particles exhibit the same molecular weight (about 245,000, as determined from the sedimentation equilibrium), contain polypeptide chains of the same two sizes (57,000 plus or minus 3,000 and 29,500 plus or minus 2,000, as determined by SDS-PAA gel electrophoresis), and have (within experimental error) the same sedimentation coefficient, isoelectric point, and amino acid composition. (ii) Isolated depolymerase and phage spikes in situ both catalyze the hydrolysis of glucosidic bonds in host capsular polysaccharide, leading ultimately to the formation of oligosaccharide fragments of one, two, and three hexasaccharide repeating units. (iii) Depolymerase 29 and phage 29 spikes have roughly the same electron optical dimensions. As tentatively estimated from the total and the virus-associated capsule depolymerase activity in the lysates, phage 29 infection seems to produce eight to seventeen times more free than incorporated spikes.