A library of 197 endophytic fungi and bacteria isolated from the Amazonian palm tree Astrocaryum sciophilum was extracted and screened for antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). Four out of five antibacterial ethyl acetate extracts were also cytotoxic for the MRC-5 cells line. Liquid chromatography coupled to tandem mass spectrometry (UPHLC-HRMS/MS) analyses combined with molecular networking data processing were carried out to allow the identification of depsipeptides and cyclopeptides responsible for the cytotoxicity in the dataset. Specific ion clusters from the active Luteibacter sp. extract were also highlighted using an MRSA activity filter. A chemical study of Luteibacter sp. was conducted leading to the structural characterization of eight fatty acid exhibiting antimicrobial activity against MRSA in the tens of µg/mL range.
In recent years, supercritical-fluid chromatography (SFC) using CO 2 as the mobile phase is expanding in the research laboratory and industry since it is considered as a green analytical method. This technic offers numerous advantages such as good separation and sensitive detection, short analysis times and stability for analytes. In this study, a method for quantification of lipids, called N-acyl homoserine lactones (AHLs), signal molecules responsible of cell-to-cell communication initially discovered in the kingdom of bacteria, by SFC coupled to high-resolution mass spectrometry (SFC-HRMS) was developed. Optimization of SFC condition together with MS ionization settings to reach the best separation and sensitivity were investigated. The established optimal analysis conditions allow quantification of up to 30 AHLs in a single run within 16 min with excellent linearity (R 2 >0.998) as well as sensitivity (pg level). This method was then applied to study AHLs production of one gram-negative endophytic bacterium Paraburkholderia sp. BSNB-0670. Nineteen known AHLs were detected, and nine abundant HSLs were quantified. To further investigate the production of uncommon AHLs, a molecular networking approach was conducted based on SFC-HRMS/MS data. This led to additionally identify four unknown AHLs annotated as N-3-hydroxydodecanoylol homoserine lactone, N-3-hydroxy-dodecadienoyl homoserine lactone (3-OH-C12:2-HSL) and two N-3-oxo-dodecenoyl homoserine lactone (3-oxo-C12:1-HSLs).
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