Transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP): Differences between their origin and vertical distributions in the ocean

The discovery of ubiquitous, abundant and transparent gel-like particles, such as the polysaccharide-containing transparent exopolymer particles (TEP) and protein-containing Coomassie stainable particles (CSP) has changed our conception of particle-organism interaction and created new questions about the origin, composition, and role of these particles in aquatic systems. Using both standard and novel staining methods, we studied these gel-like particles to determine whether CSP and TEP are sub-units of the same particle, are distinct particles with different characteristics and behaviors, or are both. Our seawater mesocosm results show that phytoplankton produce both TEP and CSP; however, their highest abundances occur at differences phases in the phytoplankton bloom. We developed a new technique for visualizing stained transparent material in unfiltered aqueous samples with the FlowCAM; this technique allows in-situ visualization and imaging of TEP and CSP in parallel stained samples. Visual examination of stained and unstained TEP and CSP from seawater microcosms, marine algal cultures, and freshwater showed that TEP and CSP have different shape, size and particle-association behavior. In a diatom-dominated microcosm, TEP concentrations were higher than CSP concentrations and unlike CSP, TEP were usually associated with diatom cells or aggregates. The cyanobacteria culture, however, showed higher CSP than TEP concentrations and aggregates of those cells appeared to be CSP-rich. Vertical and seasonal distributions of TEP and CSP in the Sargasso Sea were different. Even though both types of particles were most abundant in the upper 100 m of the water column, CSP closely followed fluorescence and total particle concentration, while the highest TEP concentration was always in the shallowest sample collected. Thus, we conclude that TEP and CSP are different particles, produced by different species at different growth phases and rates. They have different roles and are affected by different processes according to the community composition and environmental conditions.