Award: OPP-1443474

Intellectual Merit: Diatoms are a group of highly diverse microscopic marine organisms that convert light energy into cellular carbon and produce oxygen via photosynthesis. Diatoms are responsible for 40% of the carbon fixed in the ocean and a quarter of the oxygen we breathe on earth. Diatoms also are important food that sustains life amongst larger organisms in the marine food chain. In the Southern Ocean proximal to Antarctica, diatoms are an important food source for krill a favored food for whales and penguins. Diatoms are sensitive to their surrounding nutrients that they need for growth. In the Southern Ocean, most nutrients are ample but a critical nutrient for photosynthesis, iron, is at growth limiting conditions. Experiments conducted by other researchers have shown that when exogenous Fe is supplied to this region, large diatoms blooms and can carry their carbon to the deep ocean where it serves as a carbon sink. The research in this award sought to understand diatom populations, how they change in different iron concentrations and how different species are distinct in their genetic responses to iron. We worked collaboratively in a team of molecular biologists and ocean chemists to do this work. The Jenkins lab has deep expertise in molecular biology and we applied these tools to understand not only diatoms but bacteria that associate with them and may influence iron supply to the diatoms. We used methods such as molecular barcoding to delineate diatom populations, and analysis of global gene expression in lab experiments (transcriptomics) and in communities (metatranscriptomics) to understand diatom response to environmental conditions and nutrient concentrations. We found that iron along with salinity gradients structure diatom populations. We found that different diatoms remodel their metabolism in distinct ways in response to iron supply, for example modulating nitrogen metabolism. We found that distinct diatom species associate with distinct bacteria, indicating that there may be ecological stability in these associations and these bacterial associations might be part of a microbiome to help diatoms get the iron they need for growth. Our work helps us understand when a diatom species is present how it might be adapted to certain conditions and as environments change can speak to species that may become more or less prevalent under changing conditions. Species composition and function can have significant implications for the marine carbon cycle as well as food web dynamics in the Southern Ocean. Broader Impacts: This research was used as content for high enrollment microbiology courses at the University of Rhode Island. It was used to train the next generation of STEM students at the elementary school, middle school, high school, undergraduate and graduate levels. Elementary school and middle school students were brought to our lab at URI through Science and Math Investigative Learning Experience (SMILE) Fourth Grade Ecology Days and junior high Girl Scouts of Rhode Island. High School curricula and students were significantly enriched through a partnership between the Jenkins lab and the classrooms of Ms. Cara Pekarcik at N. Quincy High School in MA supported through the PolarTREC program. Ms. Pekarcik sailed on our research cruise and together we supported blogs and live streamed media accessible to her students and others through the internet. Undergraduate and Graduate students, including those from traditionally underrepresented groups in STEM were trained directly on the research in this project. Graduate students traveled to the Southern Ocean aboard the US Icebreaker Nathaniel B. Palmer and directly mentored undergraduates in the Jenkins lab prior to and after the research expedition. Last Modified: 01/14/2021 Submitted by: Bethany D Jenkins