Screening of N-Hexanamide and 2H-1,3-Benzodioxol Derivatives for Quorum Sensing Modulation in Chromobacterium violaceum
The aim of the study was screening of chemical compounds library to find “quorum sensing” modulators in proteobacteria. The library included 19 molecules that contained the N-hexanamide non-polar radical or the 2H-1,3-benzodioxole polar heterocyclic group, which were partially identical to the natural autoinductor N-hexanoyl homoserine lactone (C6-AHL) chemical structure. The Chromobacterium violaceum CV026 (NCTC 13278) was used in “quorum sensing” modulation biotests. This biosensor strain is defective in the natural autoinducer C6-AHL biosynthesis, but contains the functional homodimeric protein CviR, which, after two C6-AHL molecules reception, activates the previously silent genes transcription, including the vioABCDE operon, which leads to the production of the blue-violet pigment violacein. The direct screening showed agonistic (violacein-inducing) activity in 4 compounds and the screening variant in presence of exogenously introduced C6-AHL indicated the antagonistic (violacein-inhibiting) activity in 9 tested compounds. Interestingly, the most pronounced antagonistic activity was found in molecules that proved to be C6-AHL agonists. Significantly, the effective concentrations of these compounds required for 50% violacein inhibition were 3.2–20.4-fold lower than ones causing 50% violacein induction. In addition, the absolute concentrations of the active compounds necessary for the induction of violacein were much higher than that of a natural autoinducer, and the degree of their inhibitory effect was inversely related to the concentration of C6-AHL exogenously introduced into the biotest. According to the screening results, N-1,3-benzodioxol-5-yl-oxohexanamide was identified as the most effective “quorum sensing” modulator, submitted for further in silico, in vitro and in vivo studies.