Award: OCE-2044346

Microorganisms release small particles that contain parts of cells including lipids, proteins, metabolites, and nucleic acids. These small particles, called extracellular vesicles, therefore contain carbon that is available to other members of a food web. The intellectual merit of the project aimed to quantify the amount of organic carbon in vesicles, and to examine the role of this organic carbon in a marine food web. 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 releases a component of organic carbon to the surrounding environment in the form of extracellular vesicles. Furthermore, the amount of organic carbon in vesicles varied for different strains of Prochlorococcus, with one strain (MIT9312) encapsulating less than 1% of organic carbon in vesicles while two other strains (MED4 and NATL2A) released an average of 6% of organic carbon as vesicles. Using incubation experiments conducted in the Sargasso Sea, the project team determined that vesicles from Prochlorococcus or 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.

The project met its goals for broader impacts in a variety of activities. Undergraduate researchers were involved in scientific research at Wellesley College, graduate students were trained in the instrumentation used to quantify organic carbon concentrations, and workshops introducing early career researchers to scientific publishing were held at multiple meetings. Finally, the data generated during the project are available at public repositories enabling other scientists to reuse the data in future projects.

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, 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.

 

Last Modified: 12/22/2025
Modified by: Krista Longnecker