This 1962 study isolated twelve bacteriophages from sewage effluents of Oxford and Salisbury, England. The researchers developed a selective isolation procedure using tryptophan-supplemented media to enrich for specific phage types. All isolated phages, except Sal-1, required tryptophan for adsorption to their Escherichia coli host bacteria. Remarkably, all phages contained hydroxymethylcytosine (HMC) as a nucleic acid component and the polyamines putrescine and spermidine—properties previously known only in the T-even group of coliphages. The phages showed variable host ranges and slight morphological differences, but were generally indistinguishable by electron microscopy. The isolation of similar phage types from two geographically separate cities with independent water systems suggests these properties are widespread in urban sewage populations. The authors conclude that tryptophan-dependence and HMC content represent major distinguishing characteristics of an advanced evolutionary form of bacteriophage, extending far beyond the previously studied laboratory T-group phages.

Key findings

• Twelve tryptophan-dependent bacteriophages were isolated from sewage in Oxford and Salisbury; all except one required tryptophan for host cell adsorption
• All isolated phages contained hydroxymethylcytosine and polyamines (putrescine and spermidine), properties previously thought unique to the T-even coliphage group
• The phages showed distinct host range differences but were morphologically similar, suggesting they represent a widespread evolutionary phage family
• The same phage types were found in two geographically separated cities, indicating tryptophan-dependent phages are common in urban sewage populations