Revealing the ocean metabolome with mass spectrometry

Abstract

9All life exchanges molecules with its environment. While these metabolites are commonly 10 measured in terrestrial and limnic ecosystems, the presence of salt in marine habitats has 11 hampered quantitative analyses of the ocean metabolome. To overcome these limitations, we 12 developed SeaMet, a gas chromatography-mass spectrometry (GC-MS) method that detects 13 hundreds of metabolites down to nano-molar concentrations in less than one milliliter of 14 seawater. Using a set of metabolites dissolved in artificial seawater to benchmark our method, 15 we show metabolite signal detection increased on average across ions by 324 fold in comparison 16 to standard GC-MS methods. Our observed signal improvement occurred across tested 17 metabolite classes and provides reproducible and quantifiable results. To showcase the 18 capabilities of our method, we used SeaMet to explore the production and consumption of 19 metabolites during culture of a heterotrophic bacteria that is widespread in the North Sea. Our

Sugars dominate the seagrass rhizosphere

“…Metabolomic profiles were obtained from sediment porewaters and prepared for GC-MS using a recently described method 13 .…”

“…We measured high concentrations (on average 38.9 µM and up to 1145 µM) of organic sugars across four different types of seagrass meadows from three coastal regions (Figure 1 a,b) using a new method to detect metabolites in seawater 13 . The primary sugar in the porewater metabolome is the disaccharide sucrose, the most abundant sugar found in seagrass tissues across species 14 .…”

“…While oxygen and nitrate are limited in seagrass meadows 26 , previous reports from the Mediterranean indicate that sulfate concentrations are high (28 mM) and stable across sites and sediment depths 27 . Experiments incubating sediments with 13 C-labeled sucrose indicate microbes living underneath meadows respire between 2.083 mmol of sucrose m-2 d-1 ( Figure S3 ). Although these rates are comparatively higher than those we measured for communities living outside of the meadow (0.895 mmol of sucrose m -2 d -1 ), the community would still need 55.64 hours to completely respire the standing stock of sucrose (5 mmol in the upper 30 cm) without additional inputs from the overlying seagrasses.…”