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

Metabolomics provides an unbiased assessment of a wide range of metabolites and is an emerging ‘omics technique in the marine sciences. Here we use ‘non-targeted’ community metabolomics to determine patterns in metabolite profiles associated with particulate organic matter (POM) from two long-term monitoring stations in the western English Channel (station L4; 50° 15′N, 4° 13′W and E1; 50° 02′N, 4° 22′W). Particulates, composed of mainly phytoplankton, were sampled from the two stations during May 2009 by filtering onto glass fibre filters (> 0.7 μm to < 200 μm) from surface waters and from below thermocline. The polar metabolite fraction was measured using ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS), and the lipid fraction by direct infusion mass spectrometry (DIMS), these were then analysed to statistically compare their 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 most abundant at E1, particularly at E1-70m. Differentiated metabolites are discussed in relation to supporting data on nutrients, carbon and chlorophyll, and to metatranscriptome-derived phytoplankton taxonomy. Our results show for the first time the power of community metabolomics in discriminating metabolite patterns associated with marine POM