FIGURE 3.

Pseudomonas aeruginosa derived VSCs promote A. fumigatus growth in sulfur limiting conditions. (A) When P. aeruginosa (P.a) was inoculated on a sulfate containing inner plate it was able to trigger distal growth of A. fumigatus wild-type, ΔcysB, and ΔcysD strains on the outer S-free plates. The ΔmetF and ΔcysBΔcysD strains could not utilize P. aeruginosa derived VSCs as a sulfur source. The use of H₂S strips showed that P.a produced a small amount of H₂S on sulfate and more on methionine, but this could not cross-feed A. fumigatus. Plates were incubated at 37°C for 3 days. (B) On media containing very low cysteine (0.01 mM) as the sole S-source, both wild-type ΔcysBΔcysD strains displayed limited growth. P. aeruginosa derived VSCs significantly enhanced A. fumigatus wild-type, not mutant, growth. Plates were incubated at 37°C for 3 days. (C) Measurement of colony diameters at 36 h post-inoculation on media containing low cysteine (0.1 mM) showed that P. aeruginosa derived VSCs significantly stimulated early A. fumigatus wild-type, not mutant, growth. Plates were incubated at 37°C for 36 h. ^∗∗P < 0.01 and ^∗∗∗P < 0.001.