Marine Aggregation interactions of Prochlorococcus and Marinobacter adhaerens

The changes in marine ecological conditions brought on by warming and stratification of the oceans have radically shifted many marine environments around the globe. This project aimed to better characterize the aggregation behavior of the abundant picocyanobacterium Prochlorococcus marinus, which is hypothesized to dominate over other phytoplankton as the primary autotroph in increasingly warmer and nutrient poor oceans. This aggregation, believed to be mediated through the secretion of sticky Transparent Exopolymeric Substances (TEP), might be key for Prochlorococcus to sink throughout the ocean and serve as a source of carbon to other communities within its environment. Considering the relatively low concentration of TEP secreted by Prochlorococcus when on its own, this study explored the synergistic effect that heterotrophic bacteria and inorganic minerals in the surrounding seawater may have on the aggregation of P. marinus. This was done by inoculating P. marinus and the model heterotroph Marinobacter adhaerens HP15 individually and mixed in cylindrical roller tanks with the addition of ballasting clay minerals into roller tanks to simulate constant sinking for 7 days. The aggregates which formed after rolling were quantified and their sinking velocities and excess densities were measured. Our results indicate that the most numerous and densest aggregates formed when Prochlorococcus was in the presence of both M. adhaerens and kaolinite clay particles. I will discuss how methodology, particularly cell number, may play a role in the enhanced aggregation that I found when Prochlorococcus was cultured together with the Marinobacter.