About one-quarter of photosynthetically fixed carbon is cycled through the marine microbial community in the form of metabolites, the intermediate compounds or products of metabolic processes. Marine heterotrophic bacteria are largely responsible for consuming these metabolites as a source of carbon, energy, and nutrients, yet little is known about transporter affinity and uptake kinetics of bacteria for abundant substrates. Homarine is a small, nitrogen-containing, zwitterionic metabolite that is produced by the cyanobacterium Synechococcus as well as some diatoms and haptophytes, where it is thought to function as an osmolyte. Dissolved homarine is present in the ocean at very low concentrations (~1.1 nM in Puget Sound). I hypothesize that these low concentrations are the result of high affinity bacterial transporters for homarine. Homarine can be used as a sole carbon and nitrogen source for OBi1, a marine bacterium isolated from Puget Sound. In this study, I investigate the uptake kinetics of homarine by OBi1 in the lab using the Michaelis-Menten model. I compare the uptake kinetics of OBi1 to similar homarine uptake experiments in the Salish Sea in June 2019. I expect that OBi1 will have a high affinity for homarine uptake and will take up homarine at nanomolar concentrations. I also anticipate that the marine microbial community in Puget Sound will have similar uptake kinetics to those observed with OBi1. Understanding the uptake kinetics of homarine by marine bacteria sheds light on the cycling of homarine in marine environments like Puget Sound and can help us understand the processes that keep the dissolved homarine concentration so low.

Cyanobacteria are tiny photosynthetic microbial organisms responsible for producing roughly an eighth of the oxygen we breathe. Synechococcus is a model cyanobacteria, meaning the species has characteristics making it easy to study and modify. As a scientific community, we don’t know the function or purpose of many genes expressed by Synechococcus. The goal of this project is to determine the function of particular genes hypothesized to be important to the adaptive survival of Synechococcus in different environments. We are approaching this by building a start-to-finish gene characterization method, starting with computational analysis to identify genes of interest, followed by knocking out, or disabling these genes and observing the effect on the growth of the culture. On the computational side, I’m now analyzing residual gene expression, using that information to characterize gene clusters, and analyzing external data to infer genetic context. On the laboratory side, I’ve characterized the growth of the un-modified base strains and developed procedures for genetic modification. Identifying the function of Synechococcus genes allows scientists to better study the response of Synechococcus to varying environments, which is especially important in a changing climate. Increasing understanding of the molecular mechanisms of Synechococcus also opens the door to genome engineering for the production of biofuels, plastics, and other commodities, or for using Synechococcus as a tool for bioremedial carbon sequestration. Additionally, the genes of Synechococcus are similar to those in other related oceanic microbes such as Prochlorococcus, the most ubiquitous photosynthetic organism in the world. For all these reasons, Synechococcus is an important model organism, and a deeper understanding of its biology will bolster our sparse understanding of marine genomics.

Anthropogenic change has increased the frequency and severity of harmful algal blooms (HABs). Along the US west coast, blooms of the phytoplankton species Pseudo-nitzschia australis are proliferating, aided by anthropogenic and climatic increases in temperature and nutrient availability. P. australis produces domoic acid (DA), a neurotoxin that induces sickness and mortality in marine organisms and humans, inhibits fishery and shellfish industries, and threatens entire ecosystems. Consequently, it is vital to understand the specific conditions promoting P. australis growth and DA production. In this experiment, we determined P. australis exponential and stationary phase growth rates and DA production across a nitrogen (N) concentration gradient from 0 – 100 μM at 13 °C and 21 °C. These temperatures reflect those of upwelled water and marine heat waves respectively, processes predicted to increase with climate change. During the exponential phase, P. australis growth rates increased with N concentration, reaching maximums at 10 μM for 13 °C and 30 μM for 21 °C. Growth rates were significantly higher at 13 °C than at 21 °C during the exponential phase, except at N concentrations of 30 μM or more, where we observed similar growth rates. Although we also found positive relationships between growth rate and N concentration during the stationary phase, growth rates were lower and were not significantly different between temperature treatments. Therefore, we expect cool temperatures associated with upwelling conditions to generate faster HAB growth. We collected DA data for analysis and presentation. Based on prior research, we expect stress from nutrient limitation during the stationary phase to induce higher DA production. Thorough understanding of how anthropogenic and climatic changes impact P. australis growth and toxicity allows for accurate prediction of future HAB development and severity, thus ensuring the aquatic ecosystems sustaining not only marine life, but human industries, cultures, and societies, are preserved.

This research investigates the behavior of magnesium isotopes during the dehydration process of subducting oceanic crust. The aim is to understand how magnesium isotopes behave during the metamorphic process of subducting oceanic crust up to eclogite-facies, and whether potential magnesium isotope heterogeneity in the altered oceanic crust can be retained in the dehydrated residual eclogites. The research utilizes geochemical methods to analyze eclogites from Europe.

Specifically, this project involves the use of a Nu Plasma II multi-collector inductively coupled plasma mass spectrometer (MC-ICP-MS) to measure Mg isotopes in the rock samples. The samples are weighed and digested first, followed by column chemistry to purify the Mg fractions. The purified Mg fractions are finally measured using MC-ICP-MS to determine their Mg isotope compositions. The data will be interpreted to gain insights into the behavior of magnesium isotopes during the dehydration process of subducting oceanic crust.

Preliminary results reveal significant heterogeneity in the Mg isotope composition of the eclogites. These results have important implications for our understanding of role of oceanic crust recycling in chemical evolution of the Earth's mantle.