Membrane vesicles produced by marine bacteria: origins, distributions, and functions

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Overview: Some bacteria are known to release small amounts of their cell envelope in the form of tiny ( 200 nm diameter) spherical structures known as membrane vesicles. While the functions of these vesicles have been explored in pathogens, nothing is known about their abundance or roles in marine ecosystems. The investigators have recently demonstrated that Prochlorococcus, the numerically dominant photosynthetic cell in the world's oceans releases membrane vesicles continually during growth, and they have shown that these structures are indeed found in abundance in ocean samples. Bacterially produced membrane vesicles represent a major new feature of ocean ecosystems and could provide important clues about the network of interactions among microbes and their environment. Prochlorococcus vesicles contain diverse macromolecules, including lipids, proteins, and nucleic acids, suggesting that these structures could play many varied roles within marine microbial communities. The researchers will use the Prochlorococcus model system and the analysis of natural seawater samples from several field sites to address fundamental questions about the production and function of membrane vesicles in the oceans. The overarching questions motivating this study include: What environmental factors influence the rate of release of membrane vesicles by Prochlorococcus, and what can this tell us about the regulation of this process? How does vesicle abundance vary in different regions of the oceans? What DNA is found in vesicles from natural seawater samples? How does the vesicle "metagenome" compare to the bacterial metagenome, and what can this tell us about the diversity of organisms that release vesicles? What ecological roles might vesicles play in marine microbial ecosystems? Can they facilitate horizontal gene transfer? Can they act as a "decoy" to reduce phage predation?Intellectual Merit: Membrane vesicles represent a major new feature in ocean ecosystems. These discrete, organized structures may influence a number of biogeochemical processes, including horizontal gene transfer; moving small molecules, proteins or other macromolecules between cells; or serving as a source of fixed carbon for other bacteria. Yet we know nothing about them. This project will open this black box, and help us begin to understand the abundance and sources of membrane vesicles in the oceans, determine factors affecting their production by the numerically dominant photoautotroph Prochlorococcus, and explore aspects of their ecological roles in marine systems. With this research, the investigators will begin to establish a new area of study in marine microbial ecology that has the potential to alter current paradigms about the mechanisms through which microbes interact with both their biotic and abiotic environment.Broader Impacts: The investigators will take advantage of several avenues available at MIT to work with under-represented groups. These include: the MIT Summer Research Program, CONVERGE (a preview weekend); SEED (a Saturday education program); KEYs (a program for girls), and the MIT Edgerton Center which facilitates visits from local K-12 classes. The investigator is committed to communicating science to broad audiences. The PI has published two children's books on photosynthesis (Living Sunlight, Ocean Sunlight, Scholastic 2009, 2012; both received "best children's picture book" awards from AAAS), and is currently working on a third, on fossil fuels and climate, which will appear in 2014. This project will play a central role in the professional development of the post-doc(s) involved and data resulting from the proposed activity will be posted on public web sites, including the Prochlorococcus Portal (http://proportal.mit.edu/), and the Vesiclepedia database (http://www.microvesicles.org)