Using community metabolomics as a new approach to discriminate marine microbial particulate organic matter in the western English Channel

• First application of community metabolomics to discriminate marine POM.
• Significantly different metabolite profiles across the four English Channel locations.
• Polar metabolites most abundant in the surface waters at L4.
• Oxidised TAGs most abundant at depth at E1.

Metabolomics provides an unbiased assessment of a wide range of metabolites and is an emerging ‘omics technique in the marine sciences. We use ‘non-targeted’ community metabolomics to determine patterns in metabolite profiles associated with particulate organic matter (POM) at four locations from two long-term monitoring stations (L4 and E1) in the western English Channel. The polar metabolite fractions were measured using ultra-high performance liquid chromatography Fourier transform ion cyclotron resonance mass spectrometry (UHPLC-FT-ICR-MS), and the lipid fractions by direct infusion Fourier transform ion cyclotron resonance mass spectrometry (DI-FT-ICR-MS); these were then analysed to statistically compare the metabolite distributions. Results show significantly different profiles of metabolites across the four locations with the largest differences for both the polar and lipid fractions found between the two stations relative to the smaller differences associated with depth. We putatively annotate the most discriminant metabolites revealing a range of amino-acid derivatives, diacylglyceryltrimethylhomoserine (DGTS) lipids, oxidised fatty acids (oxylipins), glycosylated compounds, oligohexoses, phospholipids, triacylglycerides (TAGs) and oxidised TAGs. The majority of the polar metabolites were most abundant in the surface waters at L4 and least abundant in the deep waters at E1 (E1-70m). In contrast, the oxidised TAGs were more abundant at E1 and most abundant at E1-70m. The differentiated metabolites are discussed in relation to the health of the phytoplankton as indicated by nutrients, carbon and chlorophyll, and to the dominance (determined from metatranscript data) of the picoeukaryote Ostreococcus. Our results show proof of concept for community metabolomics in discriminating and characterising polar and lipid metabolite patterns associated with marine POM.