Identifying the Bacterial Community Assimilating Phosphorus in the Tropical Pacific

Benjamin Van Mooy and Krista Longnecker, Marine Chemistry and Geochemistry Department, WHOI

The tropical Pacific Ocean is characterized by low phosphorus concentrations where turnover of phosphorus is dominated by small single‐celled organisms such as bacteria. Recent changes in tropical Pacific ecosystems have increased availability of fixed nitrogen thereby shifting tropical communities to phosphorus limitation. Yet no data are available on the diversity of bacterial cells able to assimilate phosphorus which makes it difficult to interpret phosphorus fluxes through microbial communities. To address this gap, we will conduct a research project at the Hawai’i Institute for Marine Biology in Kane‘ohe Bay (21º26′N, 157º 48′W). Kane’ohe Bay has low in situ phosphorus concentrations and easy access to the water coupled with a shore‐based laboratory. The identity of bacterial cells assimilating phosphorus will be determined using field incubations with radioactive inorganic phosphorus followed by laboratory‐based molecular analysis. By identifying the diversity of bacterial cells actively involved in phosphorus cycling, we will address whether (1) all components of the bacterial community are able to assimilate inorganic phosphorus, or (2) if the ability to assimilate inorganic phosphorus is limited to a subset of the in situ bacterial community. Bacterial assimilation of phosphorus limits its availability for other organisms (e.g. phytoplankton, corals) and can alter the flux of phosphorus out of tropical surface waters. Data from the present project will increase our understanding of phosphorus cycling in the tropics where availability of phosphorus is crucial in both biogeochemical fluxes and controlling bacterial diversity.