Discipline: Biological Sciences
Vera Okolo - University of Washington
Co-Author(s): Bryndan P. Durham and E. Virginia Armbrust, University of Washington, Seattle, WA
In the surface ocean, sunlight and atmospheric CO2 are captured and fixed by autotrophic unicellular phytoplankton to generate one of the largest reservoirs of carbon on Earth, rivaling in size the global inventory of atmospheric CO2. About half of this fixed carbon is subsequently degraded by heterotrophic bacteria, a transfer that accounts for the largest flux of carbon through the ocean. Although current views of carbon transfer are rooted in the idea of passive trophic exchange, recent laboratory model system findings suggest that marine autotrophic and heterotrophic plankton interact strategically via specialized metabolites and signaling molecules. Indeed, in a speciesspecific mutualism between the phytoplankton Pseudo-nitzschia multiseries and heterotrophic bacterium Sulfitobacter sp. SA11, it was shown that the bacterial-derived plant hormone, indole-3 -acetic acid (IAA), facilitates growth in P. multiseries. In exchange, Sulfitobacter is provided with phytoplankton-derived organic substrates for growth. We hypothesize that this type of species-specific metabolite exchange is widespread in ocean communities and extends to other relatives of Pseudo-nitzschia and Sulfitobacter. Here, we have isolated six bacteria from the bacterial community of Pseudo-nitzschia pungens, a close relative of P. multiseries. Based on 16S rRNA gene sequencing, we have identified several of these bacterial associates as Sulfitobacter relatives. Identification of P. pungens-associated Sulfitobacter species further demonstrates the taxonomic linkage and potential metabolite exchange between these two taxa. As Sulfitobacter was previously shown to interact with P. multiseries and produce plant hormones, we suspect it performs a similar function with P. pungens. Further, the presence of Sulfitobacter with P. pungens provides a new opportunity to develop a model system using these two species. Using a combination of targeted metabolomics and co-culturing experiments, we will determine whether IAA, or perhaps other novel signaling molecules, are involved in the Sulfitobacter – P. pungens association and how this signaling influences the metabolism and physiology of both the bacterium and phytoplankton. We can ultimately use this new model system to understand how bacterial-phytoplankton interactions influence processes farther up the food chain, specifically how they influence carbon cycling and sequestration in the ocean. This research will ultimately lead to the fuller understanding of the marine ecosystem and, thus, our global ecosystem as a whole.
Funder Acknowledgement(s): National Science Foundation (NSF), Louis Stokes Alliances for Minority Participation (LSAMP), Genomics Outreach for Minorities (GenOM) Alliances for Learning and Vision for Underrepresented Americans (ALVA), University of Washington, and Simons Foundation.
Faculty Advisor: Virginia Armbrust,