Temperature and Ecotype Affect the Quality and Quantity of Prochlorococcus-Derived DOM

Prochlorococcus is a globally abundant and important primary producer. Because their physiology is affected by their environment, the pool of labile DOM released from these cells may influence microbial community structure and global carbon cycling. Therefore, it is imperative to learn how the composition of Prochlorococcus-derived DOM varies with the environment and how this may impact the ecosystem. Techniques used previously to study phytoplankton exudate include genomics, transcriptomics, and metabolomics. While these methods are useful, they are limited in their capacity to describe microbial interactions with DOM. We present an alternative approach for investigating exudate composition involving co-culture with auxotrophic heterotrophs to provide insight into the identity and bioavailability of compounds released. We have generated a set of auxotrophs, each dependent on one exogenously provided organic compound for growth, and co-cultured them with Prochlorococcus in a range of conditions. Preliminary results suggest that different ecotypes of Prochlorococcus release a varying array of compounds in differing amounts. Temperature has also been shown to affect exudate composition. This may indicate that the components that make up DOM released by Prochlorococcus will change based on the environment and population structure. Our bioassay has been shown to be an effective tool for studying changes in Prochlorococcus-derived DOM and a useful complement to previously used techniques.