Fig. 2: Directed evolution optimizes functional metagenomic library delivery.

a, Schematic overview of the directed evolution experiment consisting of the following steps. (1) Phage tail mutagenesis in E. coli using DIvERGE. DIvERGE is a recombineering technique that incorporates soft-randomized single-stranded (ss) DNA oligonucleotides into multiple target sites (Methods). Phage tails are encoded on packageable plasmids. (2) Infecting the E. coli with T7 lacking the tail genes (T7Δ(gp11-12-17)). This step generates mutated phage particles, each containing the cognate mutant phage-tail-encoding plasmid. (3) Selection of phage tail variants that inject DNA into the selected target cells (1–3) with improved efficiency. The selection pressure is exerted by an antibiotic against which an antibiotic selection marker is encoded on the plasmid. b, Transduction efficiencies (t.f.u. ml⁻¹) of the most efficient mutant tail fibres as compared to the parental WT tails. The target cells are Enterobacter cloacae ATCC 23355, Shigella sonnei HNCMB 25021 and E. coli NCTC 13351 as well as the phage-resistant E. coli model strain (BW25113ΔtrxAΔwaaR). Mean ± s.e.m. (n = 3 biologically independent experiments). Data are available in Supplementary Table 4.