Fig. 1: Antimicrobial activity for the complete set of peptides comprised of W and R up to 7 residues long.

a Activities are represented for peptide sequences arranged using a concentric ring chart system (referred to as ‘Harris-Clark diagrams’). Each peptide can be identified by reading the sequence from the N-terminal residue in each ring towards the C-terminal residue at the centre of the chart; inhibitory activity (IC₅₀) is indicated for that peptide by the colour of shading in the outermost compartment (i.e. the compartment identifying the N-terminal of each peptide). The three separate Harris-Clark diagrams show the inhibitory activities against S. aureus, P. aeruginosa and C. albicans. Grey sections represent peptides which did not exhibit an IC₅₀ within the range of concentrations assayed (0.8–400 µM). The two peptides which could not be synthesised are indicated by black sections with white lettering. Similar plots for MBC are shown in Supplementary Fig. 1. b Effect of peptide length on harmonic means and standard deviations for IC₅₀ and EC₅₀. Similar plots for MBC are shown in Supplementary Fig. 1. All error bars shown are ±s.d. (n = 2, 4, 8, 16, 32, 64 and 126 peptides for lengths 1–7, respectively) c Specific activities of each peptide plotted against length. Quantile regressions (90% quantile), represented by coloured lines, show the trend of specific activity with length. The solid vertical lines indicate the predicted peptide length with the greatest specific activity, and the dotted lines indicate the 95% credibility interval for this prediction generated by sampling from the posterior distribution of a Bayesian model (see Methods). The distribution of haemolytic activity for individual peptides is shown in (d) and of turbidity of 800 µM stock solutions (OD_vis) in (e), whereas (f) shows OD_vis of the same stock solutions plotted against peptide length.