Award: OCE-2049004

Microorganisms release small spherical particles that contain parts of cells including lipids, proteins, metabolites, and nucleic acids. These nanoscale structures, called extracellular vesicles, therefore contain organic carbon and other nutrients that is available to other members of a food web. The intellectual merit of this project was to quantify the amount of organic carbon in vesicles, and to examine the role of this organic carbon in marine microbial food webs. The project met this goal by first by developing the methods needed to measure the organic carbon levels in small-volume samples. The team then applied this new method to a series of laboratory cultures and field samples. The results from this portion of the project demonstrated that Prochlorococcus – the most abundant cyanobacterium on Earth, and a key player in ocean carbon cycling – releases a portion of the organic carbon it creates via photosynthesis to the surrounding environment in the form of extracellular vesicles. Vesicles represented less than 10% of all organic carbon released, but accounted for a substantial portion of the high molecular weight compounds secreted by these cells. Furthermore, the amount of organic carbon in vesicles varied among different strains of Prochlorococcus. Using incubation experiments conducted in the Sargasso Sea, the project team determined that vesicles from Prochlorococcus and the marine heterotroph Alteromonas were consumed by a distinct community of microorganisms compared to those that responded to the addition of glucose, a simple carbon source. Additional experiments using laboratory cultures provided insights into the cellular mechanisms that heterotrophs use to consume extracellular vesicles. These findings suggest that cells can utilize many different components of vesicles as a nutrient source, including lipids and proteins.

The project met its goals for broader impacts through a variety of activities. To advance scientific workforce development, undergraduate researchers were involved in scientific research at Wellesley College and the project provided opportunities for research technicians and postdoctoral scholars to learn new experimental and analytical skills. Results from the project were used to expose dozens of Wellesley undergraduates in introductory courses to concepts in marine microbial ecology such as cross-scale interactions. These data further provided the basis for new hands-on exercises to teach advanced undergraduates about biological data science and how sequencing data can be used to answer biological questions. Finally, the data generated during the project are available at public repositories enabling other scientists to reuse the data in future projects. The project has supported seven scientific publications, and we anticipate publication of two additional manuscripts in the near future. 

The pool of organic carbon in the ocean exists in a range of sizes. Extracellular vesicles are smaller than bacterial cells but larger than the individual organic molecules commonly considered as 'dissolved' organic carbon. Investigating the role of vesicles in the marine carbon cycle required both chemists and biologists, which was possible with the collaboration established for this project. Ultimately, the project’s results on how much organic carbon is in vesicles, how available this carbon is to other microorganisms, the mechanisms through which cells access this material, and the composition of the microbial community able to consume vesicles will be of interest to people investigating the role of microorganisms in the ocean and to those concerned with changes in organic carbon. These data further add to the relatively limited amount of information available concerning the functional roles of extracellular vesicles in the natural environment. 

Last Modified: 12/27/2025
Modified by: Steven Biller