Dynamic Reworking of Marine Diatom Endometabolomes

A large annual carbon flux occurs through the ocean’s labile dissolved organic carbon (DOC) pool, with carbon influx dominated by phytoplankton-derived metabolites and outflux by heterotrophic bacterioplankton uptake. We addressed the dynamics of this flux between marine primary and secondary producers through analysis of the Thalassiosira pseudonana CCMP1335 endometabolome, a proxy for labile DOC release during phytoplankton excretion and mortality. Diatom strains acclimated at one of three different temperatures (14°C, 20°C, or 28°C) were then cultured either axenically or with the bacterium Ruegeria pomeroyi DSS-3, and their endometabolites analyzed by NMR. Osmolytes were by far the most dynamic, exhibiting concentration differences up to 150-fold between conditions; median concentration variation across identified endometabolites was ~1.5-fold. Differential expression of diatom metabolic pathways suggested changes in synthesis rates as a mechanism for endometabolome remodeling. Consistent with expectations of high turnover, endometabolite mean lifetimes prior to bacterial uptake were <2 h to 12 h.