A mass spectrometric method is presented for analyzing environmental samples for the presence of extracellular signaling molecules.  These analytes are an essential part of the quorum sensing process, which is a form of density-dependent cell-to-cell communication where microbial communities produce, release, and respond to extracellular signaling molecules. The signals are produced and consumed rapidly, and their steady-state concentrations are important measures of the intensity of microbial communication in a community. Acylhomoserine lactones (AHLs) are particularly important signals for Gram-negative bacteria. Current methods for the qualification and quantification of AHLs are focused on non-specific colorimetric or luminometric bioassays.  These techniques are sensitive but are prone to interferences and curvilinear calibrations , particularly in the presence of mixtures such as sediments and soils with biofilms, where AHLs are more likely to be found. Because of these limitations there have been very few studies of the natural steady-state concentrations of AHLs. Here we report an extraction-based procedure for recovering AHLs from natural matrices preliminary to qualification and quantification by mass spectrometry. Reference standard solutions were used to develop an instrumental limit of detection. Preliminary results show signal-to-noise ratios over 150 using tandem mass spectrometry at concentrations below 10 nM (in reference sample?  soil samples?) in a reference standard. Liquid chromatography retention times show a strong correlation (r<sup>2</sup> ≥ 0.993) with the molecular weight, which can be used to predict retention times for AHLs where no standards exist. AHLs were spiked into model sediments and extracted by organic solvent, yielding initial recoveries of 2 – 16%. Extraction efficiency similarly has been observed to scale with molecular weight, indicating the potential for extraction of low nM concentrations of large molecular weight compounds.  The concentration of AHLs at several locations in the Saluda and Santee watersheds of South Carolina is presented; preliminary results indicate a natural abundance of AHLs in these surface waters of below 10nM.   <br/>

Molecular detection of acylhomoserine lactones (AHLs) in complex matrices

256th National Meeting (2018)

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