Fig. 3
Foreign supernatants containing pyoverdine can have stimulatory, neutral or inhibitory effects on the growth of receiver strains. Supernatants containing pyoverdine from donor strains were fed to receiver strains from the same community, which produced lower amounts of pyoverdine than the donors. a The growth effect of foreign supernatants on receivers varied on a continuum from high inhibition to high stimulation. The average growth effect of donor supernatants on receivers did not significantly differ between soil (yellow triangles, n = 63 strain combinations) and pond (purple circles, n = 62) isolates. Box plots depict median, first and third quartile, and the 95% confidence interval. b There was a significant positive correlation (solid black line, linear mixed model: t 38 = 5.32, p < 0.001) between the rpoD identity (i.e. relatedness) of receiver–donor pairs and the supernatant growth effect for soil, but not for pond isolates. The dashed line depicts neutral effects, whereas values greater or smaller than zero indicate cases of stimulation or inhibition, respectively, relative to conditions where receivers grew without donor supernatant. Data were ln-transformed prior to analysis
