3.3. AHL-Lactonase Activity Bioassay

The AHL-lactonase activity of AiiA_QSI-1 was quantified using Chromobacterium violaceum CV026 as an AHL-reporter strain [34]. Briefly, C6-HSL (N-hexanoyl homoserine lactone) as the substrate, different volumes of AiiA_QSI-1 were mixed with 10 µL C6-HSL (10 μM) and then dropped into the well on the LB agar plate, which was previously spread with 50 µL of overnight cultured CV026 culture. The LB plates were incubated at 30 °C for 24 h. Subsequently, the diameter of purple violacein zones appearing on the plates was measured. The residual C6-HSL concentration can be extrapolated based on a standard curve relating the C6-HSL concentration with the diameter of the violacein zone induced by CV026 culture.