Current Projects
Metal physiology of diatoms in the Southern Ocean
Marine diatoms (silicified microeukaryotes) have evolved complex traits and physiologies to survive across the global ocean. As mentioned above, phytoplankton in the Southern Ocean are confronted with multiple sources of nutrient limitation, including light, vitamin B12, iron (Fe), and manganese (Mn), limiting photosynthetic growth over time and space. Trace metals such as zinc (Zn) can be in high concentration, while Mn and Fe are too low to support maximum growth. A similar metal transport system is thought to be used for Zn and Mn, and this may result in excess Zn import into cells instead of Mn. The goal of this project is to investigate how metal physiology in Antarctic diatoms differs from temperate (North Atlantic) counterparts. Diatoms will be cultured to determine growth rates and metal requirements under a matrix of Zn and Mn. Our lab will conduct transcriptomics to determine how Antarctic diatoms structure metabolic processes under Mn stress, which metal transporters are activated, and how excess Zn is managed.
Led by Ph. D student Lizzy Wu. Collaborator: PI Nick Hawco (University of Hawaiʻi at Mānoa). Supported by NSF Office of Polar Programs
Metal physiology of phytoplankton in the tropical North Atlantic Ocean
It is presently unclear whether diverse phytoplankton replace metalloproteins containing trace metals in low supply with ones more abundant in the environment. In the tropical Atlantic, trace metal supplies vary annually with higher inputs during the summer in the form of aerosols derived from the Saharan desert plume (Arimoto et al., 1995). We are examining the relationships among iron and cobalt availability, metalloprotein abundance patterns, and biomarkers of nutritional status in the tropical Atlantic Ocean to better discern the influence of seasonally variable trace metal availability on eukaryotic phytoplankton metal metabolism. During February-March 2018, we performed shipboard mesocosm incubation experiments at three locations in the tropical Atlantic: Mauritantian Upwelling Zone (MUZ) off the coast of Cape Verde, the equatorial Atlantic, and river plume (RP)-influenced seawater off the coast of Venezuela. Eukaryotic phytoplankton blooms were induced by adding macronutrients and metals to 10 L of seawater. Metatranscriptomic and metaproteomic analyses will be used to determine which metals may have been limiting to phytoplankton growth at this site. At the ARP site, we fortuitously sampled during a diatom-diazotroph association (DDA) bloom, a symbiosis in which host diatoms contain endosymbiotic nitrogen-fixing (diazotrophic) cyanobacteria as a source of nitrogen in this typically nitrate–limited system. We plan to explore how diatoms and endosymbiotic diazotrophs restructure their nutrient acquisition or assimilation pathways and symbiotic relationship as a function of increased external nutrient supplies.
Led by postdoc Julia McGrath. Collaborators: Eric Webb (USC), Dave Hutchins (USC), Andrew Allen (JCVI), Mak Saito (WHOI). Supported by a Gordon & Betty Moore Foundation award to UGA.
Exploring continental shelf biogeochemistry & microbial ecology
Continental shelves host high levels of primary productivity and carbon export. They are natural biogeochemical gradients where biomass, nutrients, and microbial communities shift with distance from the coastline. We are interested in how changes in macronutrients, trace metals, and physicochemical parameters along shelf influence microbial metabolism and plankton ecology. This project will compare two very different continental shelf ecosystems: the South Atlantic Bight and the Gulf of Mexico. Phytoplankton will be characterized using FlowCam fluid imaging and integrated with zooplankton distributions to determine trophic level interactions. Microbial diversity and community structure will be examined with amplicon sequencing, and microbial metabolisms and interactions with the chemical environment will be interrogated with metatranscriptomics.
Led by postdocs Sean Anderson & Andrew Soborowski. Collaborators: Dan Ohnemus (SkIO), Adam Greer (SkIO), Marc Frischer (SkIO). Supported by the Simons Foundation
Shared peptides among marine microeukaryotes
Marine microeukaryotes comprise key members of the marine biosphere, performing primary production, contributing to global respiration, and acting as conduits for carbon transfer. Diverse lineages influence ocean biogeochemistry in distinct ways, for example with ciliates key consumers of plankton, diatoms major global photosynthesizers, and certain haptophytes contributing to calcite production. It is therefore insightful to examine the physiology of these groups in the natural environment using molecular (omic) signatures. Peptides may be shared among these groups due to core protein machinery being evolutionarily conserved, complicating efforts to disentangle metaproteomic signatures among microeukaryote populations in the natural environment. We are leveraging METATRYP2 software built for exploring peptide redundancy in marine prokaryotes to quantify peptide sharing across eukaryotic cultured isolates. We are finding that shared tryptic peptides are generally low among diverse cultured microeukaryotes, supporting genus-level taxon specificity.
Collaborators: Mak Saito (WHOI), Jaci Saunders (UGA)
Mixotrophy in Southern Ocean isolates
Mixotrophs are important members of the microbial community in the Southern Ocean - having the ability to both photosynthesize and consume prey through heterotrophy - and can be responsible for a large amount of microbial community grazing. The Southern Ocean appears to be the only region of the ocean where both dissolved iron (Fe) and manganese (Mn) can be in low enough in surface waters to inhibit photosynthetic growth. We hypothesize that low levels of these trace metal stimulate grazing in Southern Ocean mixotrophs as an alternative strategy to photosynthesis. To test this, the growth rates, grazing rates, and photosynthetic capabilities of three mixotrophs isolated from the Southern Ocean are being analyzed under low iron and manganese conditions in the lab. A transcriptomic analysis is being conducted which will identify metabolic signatures underpinning their trophic behavior and physiology.
Led by Ph. D student Claire Cook. Collaborators: Co-PI Nicole Millette (VIMS). Supported by NSF Office of Polar Programs
Mixotrophy and climate warming
It is unclear how mixotrophic organisms will respond to climate-induced shifts in the coming years. In particular, cell size is an important trait that has implications for the transfer of organics, carbon, and energy in the ocean On the one hand, increased temperatures may lead to increased heterotrophic rates, which could result in larger cell sizes to accommodate prey engulfment. On the other hand, photosynthetic cells generally decrease in size with warming and associated nutrient limitation to maximize nutrient efficiency. It is therefore imperative to understand how mixotroph cell size and activity will change with continued ocean warming, and what the associated impacts will be on ocean biogeochemistry.
Collaborators: PI: Suzana Leles (UTMSI). Supported by NSF Biological Oceanography.
Harmful algal blooms (HABs) in the Skidaway River
Akashiwo sanguinea captured with the Attune Cytpix
Harmful algal blooms (HABs) are known to negatively impact ecosystem health along the southeastern US, yet monitoring efforts in Georgia (GA) lag behind those conducted in adjacent states, likely resulting in an underestimation of their prevalence in the state. We have been recording cell densities of HAB species over a three year period, establishing their seasonal timing and spatial distributions, and documenting their relationship with water quality parameters in the Skidaway River Estuary. We aim to gain an understanding of the environmental conditions conducive to HAB formation by pairing FlowCAM imaging and water quality monitoring with ‘omic sequencing.
Led by Ph.D student Mallory Mintz. Collaborators: Justin Manley, Katie Higgins (GA Sea Grant & Marine Extension), Liz Harvey (UNH). Supported by SECOORA. Data on the SECOORA portal.
HABs & oyster interactions
In 2017, there was an acute oyster mortality event in the Skidaway River Estuary with 80-90% of 18-day old larvae dying after a routine water change. Brood stock and food quality were not likely to be an issue. Instead, HAB species metabolites or pathogenic bacteria were suspected. This event occurred during an Akashiwo sanguinea bloom in the estuary (Pfeiler, 2020). A. sanguinea is a dinoflagellate known to produce a harmful organic substance that can clog shellfish gills, with organics observed in tanks during the acute mortality event. This species may also produce a toxin that can harm invertebrates, and therefore may have multiple modes of toxicity. To better understand the potential for HABs to harm oysters in coastal GA, we are conducting A. sanguinea-oyster incubation experiments with the Marine Extension & GA Sea Grant Shellfish Lab. In addition, we are carrying out a field experiment in which a pool of oyster broodstock was split and deployed at two locations: the Skiaway River where A. sanguinea is known to bloom, and the Bull River, the site of a commercial aquaculture lease in which A. sanguinea status is unknown but predicted to be low. Health metrics collected over the one-year deployment will enable us to track site-specific impacts on the development of oysters. This work will directly inform aquaculture management efforts on how microbes could impair harvest efforts, and knowledge gained is relevant to growing commercial oyster shellfisheries in the southeast.
Co-PI Justin Manley (Marine Extension & GA Sea Grant), Liz Harvey (UNH). Supported by SECOORA.
HAB ecology in the southern US
The Skidaway River Estuary in Georgia hosts ephemeral blooms of A. sanguinea, while the Indian River Lagoon in Flordia hosts persistent and prolonged blooms of Aureoumbra lagunensis and Pyrodinium bahamense. It is unclear which combination of environmental factors contribute to the differences in frequency and severity of blooms between these contrasting systems, and the ecological selection processes that result in different observed bloom species between location. Our lab will conduct field sampling, mesocosm incubation experiments, and the collection of growth parameters of these HAB species through lab experiments. This information will be used to develop a biogeochemical model for southeastern US estuaries.
Led by Ph.D student Felipe Quintana. Collaborators: PI Mingshun Jiang (FAU) and Co-PI Jordon Beckler (FAU). Supported by NOAA ECOHAB.