FIG. 1.

Results of cross-feeding tests. Evidence for the production of AHLs is indicated by the expression of β-galactosidase activity (blue coloration) in the reporter strain, A. tumefaciens A136, which in each test is streaked across the top half of the plate. Production of AHLs by P. aeruginosa NSM35 (D) and A. tumefaciens KYC6 (positive control) (A) is visible. There is no evidence of AHL production by Providencia stuartii NSM71 (C) or by A. tumefaciens A136 when it was incubated with itself (negative control) (B). A weakly positive response can be seen with M. morganii NSM67 (E).