Analysis of bacterial lipodepsipeptides by matrix-assisted laser desorption/ionisation time-of-flight and high-performance liquid chromatography withelectrospray mass spectrometry

Strains of certain plant pathogenic bacteria, in particular several pathova rs of Pseudomonas syringae, are known to produce cyclic lipodepsipeptides ( LDPs) endowed with peculiar structural features and noticeable biological a ctivities. In this study, a mass spectrometry procedure is proposed for scr eening LDP-producing bacterial strains and for identifying and assessing in dividual LDPs. After matrix-assisted laser desorption/ionisation time-of-fl ight (MALDI-TOF) screening of thirteen P. syringae strains for LDP producti on, the extracts from culture filtrates of eight positive strains were subj ected to electrospray mass spectrometry for the identification of LDPs. Fiv e strains were found to produce two forms of syringomycins (SR-E and SR-G) and two forms of syringopeptin 25 (SP25A and SP25B); two strains produced S R-E, SR-G and a new form of SP22; one strain produced syringotoxin (ST) and syringostatin A (SS-A) in addition to SP25A and SP25B. The yield in cultur e of two major LPDs: SR-G (3.2-13.8 mg L-1) and SP25A (41.6-231.5 mg L-1) w as assessed by and high-performance liquid chromatography with electrospray mass spectrometry (HPLC/ESI-MS) in both scan and single ion monitoring (SI M) modes. Results of this investigation showed that the mass spectrometry p rotocol developed here is a precise and reliable method for screening bacte rial strains for LDP production and for assessing the amount of each metabo lite under various culture conditions. This could be of practical value in view of potential applications, e.g. biocontrol of post-harvest fungal dise ases. Copyright (C) 2001 John Wiley & Sons, Ltd.