Fig. 1

Identification of N-(3-hydroxy-octanoyl)-homoserine lactone (3OH,C8-HSL) in culture supernatants of strain P4. An ethyl acetate extract of a spend culture supernatant was concentrated, resuspended in 100 % acetonitrile and analyzed by UPLC MS/MS. Panel a: elution profile of synthetic 3OH,C8-HSL. Panel b: mass spectra of synthetic 3OH,C8-HSL. The m/z values 244, 226 and 102 correspond to the protonated forms of 3OH,C8-HSL (243 + 1), the dehydrated 3OH,C8-HSL (225 + 1) and the characteristic amine substituted lactone cycle (101 + 1), respectively. Panel c: elution profile of the concentrated culture supernatant of strain P4. The major peak migrates as the one of synthetic 3OH,C8-HSL. Panel d: mass spectrum of the major peak observed in the concentrated culture supernatant of strain P4. The m/z values and species are identical to those observed for synthetic 3OH,C8-HSL