(145b) Effects of Engineered Nanoparticles On the Assembly of Exopolymeric Substances From Marine Phytoplankton

Primary production of marine phytoplankton, ranges from 35 to 65 gigatones of carbon per year, representing about half of photosynthesis production on earth and plays a critical role in global carbon cycle. Exopolymeric substances (EPS), composed of polysaccharide-rich anionic colloidal polymers, are released into water column from marine phytoplankton during photosynthesis. The major portion (40~60 %) of fixed carbon in phytoplankton is released as EPS to contribute significantly to the dissolved organic carbon (DOC) pool in the ocean. In addition, aggregation of EPS has been proposed to be an important pathway to convert DOC into particulate organic carbon (POC). The sinking of those POC particles mediates vertical carbon fluxes from the ocean surface to the deep sea. Recent studies have identified that EPS can self-assemble into microgels (POC) through hydrophobic and ionic interaction mechanisms.

Engineered Nanoparticles (ENs), which range in size from 1 to 100 nm, have properties that are very different from those of bulk materials of the same chemical composition. Although ENs are widely used, the impacts of these materials on marine environments are largely unknown. Here we study the the interactions of various ENs and EPS from several representative phytoplankton species. We used a marine diatom Amphora sp. and a marine bacterium, Sagittula stellata, as preliminary model organisms. In this study, nanoparticles with different size and surface modifications (e.g. hydrophobicity; surface charge) were mixed with EPS samples, and the assembly of EN-EPS was monitored by measuring the average microgel size for 10 days. We found that only hydrophobic ENs can significantly accelerate the assembling process of Sagittula stellata EPS. Conversely, ENs regardless of surface modifications can facilitate the assembly of Amphora EPS. The results suggest that ENs released into the aquatic system can influence the kinetics of EPS assembly process that could further interfere with the ocean carbon cycle. Our data also indicated that the effects of ENs on EPS assembly kinetics vary depending on the EPS chemical composition. The EN-induced changes of EPS assembly may lead to unexpected disturbance in elementary cycling and possible undesired selection pressure in marine ecosystem. (Supported by NSF CBET-0932404 and CITRIS #31 seed grant)