Fig. 2. Identification of phage defence systems.
a, Left: schematic of the ‘tab’ selection method. At intermediate concentrations of phage, tab selection facilitates the survival of cells with either abortive infection or direct defences. Right: examples of T4 selection plates for cells containing the fosmid library or an empty vector control. b, Left: tenfold dilutions of λvir phages on lawns of a sample of 15 positive clones from the λvir screen. Multiple phenotypes were observed, including reduction of plaquing with individual escape plaques indicative of a restriction-modification system; no lysis at any concentration of phage typically reflecting a loss of adsorption; or reduction of plaquing, generally indicative of a phage defence system. Right: examples of fosmid inserts corresponding to exemplar phenotypes in b (left), with relevant genes coloured. c, Examples of read coverage (100 bp moving average) from deep sequencing of sub-libraries generated from positive fosmid clones, with maxima delineating defence system candidates. Genes were coloured or shaded as indicated at the top. d, Summary counts of defence systems identified.