Thalassiosira weissflogii attachment assay and phylogenetic affiliation of bacterial isolates from samples of the German Wadden Sea

Aggregation of algae, mainly diatoms, is an important process in marine systems leading to the settling of particulate organic carbon predominantly in the form of marine snow. Exudation products of phytoplankton form transparent exopolymer particles (TEP), which acts as the glue for particle aggregation. Heterotrophic bacteria interacting with phytoplankton may influence TEP formation and phytoplankton aggregation. This bacterial impact has not been explored in detail. We hypothesized that bacteria attaching to Thalassiosira weissflogii might interact in a yet-to-be determined manner, which could impact TEP formation and aggregate abundance. The role of individual T. weissflogii-attaching and free-living new bacterial isolates for TEP production and diatom aggregation was investigated in vitro. T. weissflogii did not aggregate in axenic culture, and striking differences in aggregation dynamics and TEP abundance were observed when diatom cultures were inoculated with either diatom-attaching or free-living bacteria. The data indicated that free-living bacteria might not influence aggregation whereas bacteria attaching to diatom cells may increase aggregate formation. Interestingly, photosynthetically inactivated T. weissflogii cells did not aggregate regardless of the presence of bacteria. Comparison of aggregate formation, TEP production, aggregate sinking velocity and solid hydrated density revealed remarkable differences. Both, photosynthetically active T. weissflogii and specific diatom-attaching bacteria were required for aggregation. It was concluded that interactions between heterotrophic bacteria and diatoms increased aggregate formation and particle sinking and thus may enhance the efficiency of the biological pump.

Hydrostatic pressure affects aggregate transformation and organic carbon transport: in and beyond the twilight zone: Experiment December 2010

This work aimed to explore evaluated the effects of the increased of hydrostatic pressure on a defined bacterial community on aggregates formed from an axenic culture of marine diatoms by simulating sedimentation to the deep sea by increase of hydrostatic pressure up to 30 bar (equivalent to 3000 m water depth) against control at ambient surface pressure. Our hypothesis was that microbial colonization and community composition and thus microbial OM turnover is greatly affected by changes in hydrostatic pressure during sinking to the deep ocean.