Award: OCE-2029738

Diatoms (Bacillariophyceae) are unicellular photosynthetic algae, accounting for about 40% of total marine primary production (equivalent to terrestrial rainforests) and critical ecological players in the contemporary ocean. Diatoms can form enormous blooms in the ocean that can be seen from space and are the base of food webs in coastal and upwelling systems, support essential fisheries, and are central to the biogeochemical cycling of important nutrients such as carbon and silicon. Over geological time, diatoms have influenced the world's climate by changing the carbon flux into the oceans. Diatoms are generally analyzed in bulk, specifically bulk gene expression measurements, which generate a valuable analysis of the population's average functioning; however, they fail to show how each individual diatom cell contributes to the population characteristics and confound cell variability and stages in heterogeneous populations. Single-cell gene expression measurements allow for examining the molecular mechanisms and stages involved in state transitions, has been challenging to implement with marine samples. Single-cell gene expression measurements in thousands of individual diatom cells provide a quantitative and ultrahigh-resolution picture of the population's transient cell states and allow assessment of cell heterogeneity within a population—a new dimension in diatoms and phytoplankton in general. Such analyses facilitate and expose signatures of cell state instability that precede critical transitions, which can lead for example, to population collapse and carbon sequestration. We have integrated measurements within established systems biology and bioinformatics approaches to provide an understanding of phytoplankton responses and critical transitions to nitrogen limitation and starvation and new environmental perturbations driven by climate change. Specifically, we improved single-cell diatom protocols and achieved a technological breakthrough with the transcriptomic profiling of individual diatoms under nitrogen limitation. With this ability, we have discovered functional heterogeneity at the single-cell level in the model diatom Thalassiosira pseudonana (Thaps), transitions between day and night states, and nitrogen-replete and nitrogen-starved states. This discovery will allow us to answer critical questions regarding population resilience and transitions into different phenotypes as diatoms respond to climate change. We disseminated high-school curriculum and supported teachers and summer student interns. We trained high school educators in marine science and inspired educators to encourage the next generation of diverse and scientifically informed students and scientists. We also made the broader public aware by bringing cross-disciplinary concepts to classrooms that promoted critical thinking around fundamental systems biology concepts, state transitions, carbon sequestration, and the microbial loop. Furthermore, we participated in developing and implementing a leadership in STEM program, "Leadership Empowerment and Development in STEM (LEADS)." Finally, we brought together a focus group of students through our Environmental Systems in the Outdoors Research Program. We learned that students are intrigued by the cutting-edge single-cell techniques used in this scientific project. Students' intrigue was enhanced by the realization that cell transitions such as cell death is a phenomenon that transcends the fields of cancer, population ecology, and climate change. Furthermore, perhaps most importantly, these topics provide students hope and optimism, which are needed in today's classrooms. Last Modified: 10/19/2023 Submitted by: Monica V Orellana