The identification and quantification of molecules involved in bacterial communication are major prerequisites for the understanding of interspecies interactions at the molecular level. We developed a procedure allowing the determination of 2-heptyl-4(1H)-quinolone (HHQ) and 2-heptyl-3-hydroxy-4(1H)-quinolone (PQS) and the virulence factor pyocyanin (PYO) formed by the Gram-negative bacterium Pseudomonas aeruginosa. The method is based on dispersive liquid-liquid microextraction from small supernatant volumes (below 10 μL) followed by quantitative matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS). The use of ionic liquid matrix led to a lowered limit of detection for pyocyanin and, due to suppression of matrix background signals, easy to interpret mass spectra compared to crystalline matrices. Using an isotope-labeled pyocyanin standard synthesized in small-scale synthesis, quantitative analysis spanning approximately one order of magnitude (0.5 to 250 fmol) was feasible. The method was successfully applied to the detection of the signaling molecules PQS and HHQ in cultures of P. aeruginosa strains isolated from sputum of cystic fibrosis patients and allowed a highly sensitive quantification of PYO from these cultures. Hence, the developed method bears the potential to be used for screening purposes in clinical settings and will help to decipher the molecular basis of bacterial communication. Graphical abstract Ionic liquid matrices for the detection and quantification of the toxin pyocyanin and other signaling molecules from P. aeruginosa by MALDI MS.
Keywords: Biofilm; Cystic fibrosis; Pseudomonas aeruginosa; Pyocyanin; Quorum sensing; Resistance.