The opportunistic human pathogen Serratia marcescens AS-1 produces the N-hexanoylhomoserine lactone (C6HSL) receptor SpnR, a homologue of LuxR from Vibrio fischeri, which activates pig clusters to produce the antibacterial prodigiosin. In this study, we attempted to artificially regulate quorum sensing (QS) by changing the role of SpnR in N-acylhomoserine lactone (AHL)-mediated QS. SpnR was obtained as a fusion protein tagged with maltose-binding protein (MBP) from overexpression in Escherichia coil, and its specific affinity to C6HSL was demonstrated by quartz crystal microbalance analysis and AHL-bioassay with Chromobacterium violaceum CV026. Prodigiosin production was effectively inhibited by externally added MBP-SpnR in both wild-type AS-1 and the AHL synthase-defective mutant AS-1(Delta spnl). For the mutant, the induced amount of prodigiosin was drastically reduced to approximately 4% with the addition of 18 mu M MBP-SpnR to the liquid medium, indicating 81% trapping of C6HSL. A system for inhibiting QS can be constructed by adding exogenous AHL receptor to the culture broth to keep the concentration of free AHL low, whereas intracellular SpnR naturally functions as the activator in response to QS. (C) 2016 Elsevier Inc. All rights reserved.