Fig. 1

Pyoverdine production and growth of natural Pseudomonas isolates. The natural soil (a, n = 158) and pond (b, n = 157) isolates varied greatly in their levels of pyoverdine production. Pyoverdine production was measured in iron-limited casamino acids (CAA) medium, and was scaled relative to the production levels of characterised laboratory reference strains (Supplementary Table 1). c There was a significant positive correlation (solid line) between growth of the isolates in iron-limited media and their pyoverdine production level, suggesting that pyoverdine is important for growth. Values are given as means across three replicates for soil (yellow triangles) and pond (purple circles) isolates. Dotted lines denote growth and pyoverdine production of reference strains. d While the growth of natural isolates was strongly limited in media with low iron availability, all strains grew well when iron (40 µM FeCl₃) was added. This demonstrates that all natural isolates could use CAA as a nutrient source. Box plots show the median, first and third quartile, and the 95% confidence interval