Intra- and extracellular metabolomics reveal new dimensions of Prochlorococcus activity over diel light/dark cycles

Prochlorococcus, the dominant phytoplankton in oligotrophic oceans, synchronizes with daily changes in light availability and thus displays diel rhythmicity in its cell cycle, transcriptome, and proteome. This synchronization has significant implications for downstream ecosystem function and carbon cycling, as heterotrophic organisms respond to daily fluctuations in fixed organic carbon. However, exudation and cross-feeding are difficult to predict from sequence-based data, and diel rhythms of exudation have not been characterized in Prochlorococcus. To address this gap, we took a metabolomics approach to characterizing Prochlorococcus (strain MIT9301) cultures grown under a diel light/dark cycle. We sampled for intra- and extracellular metabolites, and made use of multiple new methods (aniline and benzoyl chloride derivatization) for measuring previously unquantified extracellular metabolites. We found that both intracellular and extracellular metabolite concentrations displayed diel rhythmicity, allowing us to make molecule-specific and temporally resolved connections between Prochlorococcus activity and released labile carbon. We also found evidence that Prochlorococcus reassimilates metabolites which it previously released into solution. This reassimilation may be a means of retaining nutrients like nitrogen or phosphorous, and could generate competition between Prochlorococcus and co-occurring heterotrophic microbes for released Prochlorococcus metabolites. Together this work expands our understanding of Prochlorococcus physiology and marine carbon cycling. 

Presentation Preference: Oral

Primary Presenter: Kathryn Halloran, Woods Hole Oceanographic Institution (khhalloran@gmail.com)

Authors:

Kathryn Halloran, Woods Hole Oceanographic Institution  (khhalloran@gmail.com)

Brianna Garcia, Woods Hole Oceanographic Institution  (brianna.garcia@whoi.edu)

Natalie Graham, Woods Hole Oceanographic Institution  (natalie.graham@whoi.edu)

Rogier Braakman, Massachusetts Institute of Technology  (braakman@mit.edu)

Eli Salcedo, Massachusetts Institute of Technology  (esalcedo@mit.edu)

Allison Coe, Massachusetts Institute of Technology  (a_coe@mit.edu)

Melissa Kido Soule, Woods Hole Oceanographic Institution  (msoule@whoi.edu)

Sallie Chisholm, Massachusetts Institute of Technology  (chisholm@mit.edu)

Elizabeth Kujawinski, Woods Hole Oceanographic Institution  (ekujawinski@whoi.edu)