MALDI-IMS Detection of Pyoverdine

MALDI-IMS allows us to detect pyoverdine (m/z 1044) on the surface of the agar plate, as reported in a previous study [11 (link)]. The ion distribution of pyoverdine on the surface of iron-limited agar plates revealed a difference in densities of pyoverdine between wild type and mutants of P. taiwanensis. The iron-limited agar samples with bacterial colonies were excised and placed on glass slides, and then covered with a thin layer of universal MALDI matrix (Sigma-Aldrich). Samples were detected in positive reflectron ion mode, and screened at 200 μm laser intervals with the acquisition mass range set at 1000–1500 Da. The standard peptide calibration mixture (Peptide Calibration Standard 206,195, Bruker, 1000–3200 Da) and universal MALDI matrix were used to calibrate and test the MALDI-TOF mass spectrometer. The IMS data were analyzed using Fleximaging 3.0 software (Bruker, Billerica, MA, USA). The intensity of the molecules is presented as gradient colors in the figures.