Signaling molecules from Lactuca sativa L. induced quorum sensing phenotypes in bacteria

The outcome of the present investigation revealed that lettuce (Lactuca sativa L.) extract strongly interferes with acyl homoserine lactone (AHL) regulated physiological functions in the bioreporter strain, Chromobacterium violaceum CV026. Extracts of L. sativa also promoted production of virulence factors in plant pathogen, Pectobacterium carotovorum, and significantly increased tissue maceration on potato tubers when there was a low concentration (103 cfu · ml–1) of the bacterium was used. The thin layer chromatogram which visualised with AHL bioreporter strain, CV026, showed that L. sativa extract produced a circular spot with a diffuse edge tail and migrated with the same mobility as standard N-hexanoyl-L-homoserine lactone (C6-HSL). Gas Chromatography Mass Spectroscopy (GC-MS) analysis of the lettuce extract resulted in the identification of 19 compounds of which homoserine was identified for the first time in plants. Homoserine accounted for 2.37% of the total constituents. It is a new finding that lettuce contains AHL like substances (homoserine) which excite AHL related quorum sensing (QS) in bacteria.