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

Jacqueline Comstock, University of California Santa Barbara, Ecology, Evolution, and Marine Biology, Santa Barbara, CA, United States, Craig Nelson, University of Hawaii at Manoa, School of Ocean, Earth Science, and Technology, Honolulu, HI, United States, Andreas Haas, Royal Netherlands Institute for Sea Research, Marine Microbiology & Biogeochemistry, Den Burg, Netherlands, Linda Wegley Kelly, San Diego State University, Department of Biology, San Diego, United States, Irina Koester, University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, Zachary Quinlan, San Diego State University, Department of Biology, San Diego, CA, United States and Craig A Carlson, University of California Santa Barbara, Marine Science Institute/Department of Ecology, Evolution and Marine Biology, Santa Barbara, CA, United States
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.