FIG. 4.

Effect on lactone production by the TTSS and Act of A. hydrophila SSU. WT A. hydrophila, its various mutants, and complemented strains were grown to various densities (OD₆₀₀ of 0.3 to 1.2). The cultures were centrifuged, and the supernatants were measured for β-galactosidase activity (presented in Miller units), indicative of AHL production, using an A. tumefaciens β-galactosidase reporter strain. Three to five independent experiments were performed, and the arithmetic mean ± deviation was plotted. Single asterisks denote statistically significant differences (by Student's t test) in lactone production between WT and its various mutant derivatives at an OD of 1.2. A double asterisk denotes a statistically significant difference in lactone production in WT and its act mutant at ODs of 0.9 and 1.2. The increase in lactone production by the complemented strains was significantly higher than that in the corresponding mutants but was statistically insignificant compared to lactone production in the WT bacterium. Strains designated act⁺ and aopB⁺ indicate complementation of the corresponding mutants. The actual P values are presented in the text. Compl, complementation.