Fig. 3: The facilitation of spatial expansion in a pairwise coculture of hospital sink isolates, Bp and Pa22.

Bp: Bacillus paranthracis, Pa22: Pseudomonas aeruginosa 192622, CB: Carbenicillin. Source data are provided as a Source Data file. a Pa22 tolerated CB treatment better than Bp. Liquid media were inoculated with Bp (red) or Pa22 (light blue) at OD₆₀₀ = ~2.1×10⁻⁵ (from dilutions of a cell suspension with OD₆₀₀ > 0.05), without (top) or with CB (10 μg ml⁻¹, bottom). Curves and shades show average and standard deviation, respectively, from n = 2 biological replicates, each with three technical replicates. b Pa22 dominated Bp in well-mixed cocultures. Liquid media were inoculated with a 1:1 mixture of the two species at OD₆₀₀ = ~2.1×10⁻⁵, incubated for 27 h, and then plated to determine relative abundances (Supplementary Fig. 21b). Bars and error bars represent mean and standard deviation from n = 2 independent experiments (symbols) after averaging technical replicates (solid/open/lined markers). c Pa22’s range expansion was suppressed by CB treatment and rescued by Bp. 20 ml of swarming agar (0.55%) media were inoculated with 1 μl of Bp or Pa22 at OD₆₀₀ = ~0.43 with or without CB (10 μg ml⁻¹). Dishes were imaged at 24 h, processed, and analyzed for colony areas using a custom Python script (Methods). Images shown were equally adjusted for brightness/contrast. Dish diameter: 100 mm. Raw images from n = 2 independent replicates are in Supplementary Fig. 19. d The rescue of the coculture range expansion occurred at the expense of Bp’s growth. In the same experiments as in (c), media were center inoculated with 1 μl of 1:1 mixture of the two species at OD₆₀₀ = ~0.43 (circles) or ~0.34 (triangles). The dishes were imaged after 24 h (see Supplementary Fig. 19 for raw images). Then, whole colonies were harvested with 5 ml of saline, and relative abundances were estimated by plating (Supplementary Fig. 21b). Bars and error bars show mean and standard deviation of n = 2 independent experiments (symbols) after averaging technical replicates (solid/open markers). Images shown were equally adjusted for brightness/contrast. Dish diameter: 100 mm.