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Overview:Diatoms, unicellular, eukaryotic photoautotrophs, are one of the most ecologically successful and functionally diverse organisms in the ocean. Despite accounting for <1% of Earth’s biomass, diatoms are estimated to contribute ~20% of total global primary productivity. In addition to being a key component of the global carbon cycle, diatoms are also tightly connected to silicon (Si) biogeochemistry because of their obligate requirement of Si for cell wall formation and growth. It is estimated that diatoms process over 240 Teramoles of biogenic silica each year and that each molecule of silicon is cycled through a diatom 39 times before being exported to the deep ocean. This proposal seeks to understand Si regulation of diatom productivity in the sea at the molecular level through a unique combination of state of the art tracer methods and assessments of silicon transporter expression and diversity. Success will provide new insights into the physiological basis of Si limitation in the sea and the molecular mechanisms involved.
Intellectual Merit:Decades of oceanographic and field research has provided detailed insight into the dynamics of silicon uptake and silica production in natural populations, but a molecular understanding of the factors that influence silicification processes is required for further understanding the regulation of silicon and carbon fluxes in the ocean. Proposed research will build upon these studies by coupling classical measurements of silicon uptake and silica production with molecular analyses of genes and proteins involved in silicification. Characterizing the genetic potential for silicification can provide new information on the factors that regulate the distribution of diatoms and influence in situ rates of silicon uptake and silica production. Our proposed study site off the coast of California is a region where diatom dynamics are well-characterized and silica production is among the highest in the world. Episodic upwelling from May through September creates a high probability of diatom bloom conditions. Low Fe conditions also occur in this same region allowing the known linkages between Fe stress and diatom silicification to be explored at the molecular level. Our proposed cruise track will target gradients in silicic acid and Fe concetrations with the following goals: 1) Characterize the expression pattern of known genes involved in silicification (Silicification-related genes; SiRGs) 2) Correlate SiRG expression patterns to Si concentrations, silicon uptake kinetics, and silica production rates, 3) Develop a method to normalize uptake kinetics and silica production to SiRG expression levels as a more accurate measure of diatom activity and growth, and 4) Characterize the diel periodicity of silicon uptake kinetics, silica production, and SiRG expression. This research is expected to provide significant information about the molecular regulation of silicification in natural populations and improve our knowledge on the factors controlling the distribution and productivity of diatoms in the ocean.
Broader Impacts.Proposed research blends concepts in physiology, genomics, molecular biology, and biochemistry with marine ecology and oceanography, providing an opportunity for researchers with diverse interests to interact. This project provides an opportunity for a female researcher to get first time PI experience and, at the same time, provides excellent hands-on, cross-disciplinary training for a graduate student. In addition, underserved and underrepresented undergraduate students will serve as an integral component of the lab-based research and will have an opportunity to participate in the proposed oceanographic research cruises. To further facilitate outreach, students participating in field work will write a daily blog describing their experience and life at sea. In support of fostering exposure of a broad audience to Science Technology Engineering and Mathematics areas, we will leverage existing resources both at Rutgers’ and UC Santa Barbara to develop novel methods for translating scientific themes and data sets generated from field work into innovative teaching materials aimed at K-12 educators, K-12 students, and undergraduates.