Technical agar

The bacterial strains used in this study are listed in Key resources table. For each experiment, all strains were grown in Luria broth (LB; Thermo Fisher Scientific, USA) for 18 hr to stationary phase at 37°C with shaking (180 r.p.m.). For routine culture of bacteria on solid media, strains were grown on LB supplemented with 1.5% technical agar (BD Biosciences, USA). Liquid and solid growth media were supplemented with tetracycline (12.5 μg ml⁻¹; Sigma-Aldrich, USA) and isopropyl-β-D-thiogalactoside (IPTG, Melford Laboratories, UK; used at 0.5 mM unless stated otherwise) where required. Enumeration of bacterial c.f.u. was done by plating 10-fold serial dilutions of bacterial cultures on to Mueller-Hinton agar (MHA; Thermo Fisher Scientific) plates. Inoculated agar plates were incubated statically for 18 hr in air at 37°C.

The E. coli strains used in this study are listed in Table 1. Bacterial strains were grown at 37 °C with shaking [180 rotations per minute (r.p.m.)] for 18 h to stationary phase in Luria–Broth (LB; Thermo Fisher Scientific, USA). For culture on solid media, bacteria were grown on LB supplemented with 1.5 % technical agar (BD Biosciences, USA). Bacterial c.f.u. were quantified by serial tenfold dilution of bacterial cultures and plating onto Mueller–Hinton broth (MHB; Sigma-Aldrich, USA) supplemented with 1.5 % technical agar. Agar plates were incubated statically in air for 18 h at 37 °C.