gms | German Medical Science

The brown seaweed Fucus vesiculosus, also known as ‘bladderwrack’, is widely distributed and abundant in the Baltic Sea. In a recent study, we mapped the surface microbiome of the Baltic Fucus vesiculosus and analyzed, comparatively, the metabolome of its surfaces and inner tissues by UPLC-MS/MS and DESI-mass spectrometry imaging for the first time [1]. The metabolome of Fucus vesiculosus holobiont was rich, hence we investigated seasonal variations in the metabolome and its potential relation to its bioactivity profile. By using a definitive screening design combined with pressurised liquid extraction, an optimised extraction protocol was developed. Many compounds were found to vary with the sampling month; phlorotannin total ion count (TIC) was highest in summer, whilst chlorophylls, lipids, and carotenoids peaked in winter and spring. The Methicillin-resistant Staphylococcus aureus (MRSA) inhibitory activity was however consistent year-round without a clear seasonal trend [2]. In order to identify and purify compounds responsible for antimicrobial activity of Fucus vesiculosus in a targeted manner, we applied the UPLC-QToF-MS/MS-based ‘bioactive molecular networking‘ (BMN) concept on the most bioactive n-hexane and n-butanol subextracts of Baltic F. vesiculosus coupled with in silico dereplication tools for targeted isolation and characterization the compounds responsible for antimicrobial activity. The first antimicrobial cluster identified by BMN was galactolipids. Our targeted isolation efforts for this class led to the isolation of six monogalactosyldiacylglycerol (MGDG) derivatives and one digalactosyldiacylglycerol. Several MGDGs and the DGDG exhibited antimicrobial activity. The second compound class with high bioactivity was phlorotannins. Particularly, phlorethol-type phlorotannins showed high correlations with antimicrobial activity based on the BMN approach, and two phlorotannins were isolated. This study shows that antimicrobial components of F. vesiculosus are algal membrane-bound and that automated tools such as BMN provides a complementary tool for targeted isolation of bioactive metabolites.

Keywords: Fucus vesiculosus, pressurised liquid extraction, untargeted metabolomics, seasonal variations, bioactive molecular networking, bioactivity