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Accurate mass analysis of N ‐acyl‐homoserine‐lactones and cognate lactone‐opened compounds in bacterial isolates of Pseudomonas aeruginosa PAO1 by LC‐ESI‐LTQ‐FTICR‐MS
Author(s) -
Cataldi Tommaso R. I.,
Bianco Giuliana,
Abate Salvatore
Publication year - 2009
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.1479
Subject(s) - chemistry , lactone , homoserine , mass spectrometry , quorum sensing , tandem mass spectrometry , mass spectrum , stereochemistry , chromatography , biochemistry , virulence , gene
Abstract N ‐acyl‐homoserine‐lactones (AHSLs) are widely conserved signal molecules present in quorum sensing systems of Gram‐negative bacteria such as Pseudomonas aeruginosa . We present here the results obtained with a hybrid linear trap/Fourier transform ion cyclotron resonance (LTQ‐FTICR) mass spectrometer used to investigate the occurrence of AHSLs and cognate N ‐acyl‐homoserines (AHSs) in bacterial isolates of P. aeruginosa (strain PAO1). Two hydrolysed AHSs were found in significant amounts, most likely formed through the lactone opening of N ‐3‐oxo‐decanoyl‐ L ‐homoserine‐lactone (3OC 10 ‐HSL) and N ‐3‐oxo‐dodecanoyl‐ L ‐homoserine‐lactone (3OC 12 ‐HSL). Structure elucidation of these ring‐opened molecules, i.e. N ‐3‐oxo‐decanoyl‐ L ‐homoserine (3OC 10 ‐HS), and N ‐3‐oxo‐dodecanoyl‐ L ‐homoserine (3OC 12 ‐HS), which are not detected by bacterial biosensors, was performed by high‐resolution and accurate mass measurements upon liquid chromatography (LC) and confirmed by tandem MS in the LTQ analyser. Assignment of chemical formula, with mass spectra in the form of [M + H] + , was significantly expedited by extracted ion chromatograms (XICs) because the number of potentially plausible formulae for each protonated signalling molecule was considerably reduced a priori by the LC behaviour, the high mass measurement accuracy available in FTICR mass spectra and the isotopic patterns. At least two concentration levels were observed in spent culture supernatants of P. aeruginosa : compounds at a relatively high content (5–15 µ M ) that is C 4 ‐HSL, 3OC 10 ‐HS, and 3OC 12 ‐HS and those occurring at a lower content (<0.2 µ M ) that is C 6 ‐HSL and C 8 ‐HSL. The implications of this work extend to a great variety of Gram‐negative bacteria. Copyright © 2008 John Wiley & Sons, Ltd.