Application of a novel method for the quantification of dissolved metabolites to diatom culture media and oligotrophic seawater

Marine microbes both require and produce dissolved organic matter (DOM) through their metabolic and growth processes. Of the large, diverse DOM pool, many small, polar molecules are highly bioavailable and cycle rapidly in the marine environment. However, little is known about the fate of these molecules, largely because of methodological hurdles in measuring their dissolved concentrations. For example, sulfonate-containing molecules, including 2,3-dihydroxypropane-1-sulfonate (DHPS) and isethionate, have been implicated in key phytoplankton-bacterial interactions but cannot be accurately quantified in the dissolved phase using current methods. These and other small, polar compounds are not well extracted from seawater and are therefore not available for identification and quantification by mass spectrometry. We have developed a novel method whereby these compounds are derivatized prior to extraction with a PPL solid-phase resin and detected via liquid chromatography mass spectrometry (LC-MS). With this method, we are able to extract and quantify DHPS, isethionate, and 50 other metabolites that were not accessible to previous methods. We present results on the dynamics of previously undetected polar metabolites in phytoplankton-bacteria co-cultures and in oligotrophic seawater from the Bermuda Atlantic Time-series Study site. These methodological improvements are leading to a better understanding of marine microbial community and ecosystem interactions.