Tracking microbial uptake of phytoplankton derived DOM and model compounds by coral reef bacterioplankton using stable isotope probing

Coral reefs are highly productive ecosystems in tropical and subtropical oligotrophic environments where heterotrophic microbial dynamics are dominated by bacterioplankton recycling of dissolved organic matter (DOM). Bacterioplankton are the primary consumers of DOM and act as a trophic conduit. Linking bacterioplankton community structure with DOM utilization is important for understanding bacterioplankton niche partitioning and element cycling. We conducted two DNA stable isotope probing (SIP) experiments using Mo’orea backreef water to track differential incorporation of DOM of various qualities and quantities. Amendments included ¹³C labeled Synechococcus -derived DOM of varying lability and ¹³C labeled model compounds of different quantities. The Synechococcus-derived compounds included a cell lysate and an exudate that had been concentrated on a solid phase extraction (SPE) column. The model compound mannose was added in two different concentrations to investigate the influence of dosage on microbial response and DOM uptake. All amendments stimulated bacterioplankton growth relative to the control treatments. Greater change in bacterioplankton abundance was observed in the phytoplankton-derived incubations with lysate and model compounds compared to the SPE exudates. Communities responding to amended DOM sources exhibited significantly different microbial communities between treatments. While response of copiotrophic taxa were observed in all amendments, incorporation of labeled DOM was also observed in more diverse taxa. We will present data on the variable uptake of DOM by bacterioplankton along with changes in DOM concentration and composition to provide further insight into the roles of different bacterioplankton in niche partitioning and carbon cycling over coral reefs.