Snow algae communities on stratovolcanoes of the Pacific Northwest The majority of geomicrobiological research conducted on glacial systems to date has focused on glaciers that override primarily carbonate or granitic bedrock types, with little known of the processes that support microbial life in glacial systems overriding volcanic terrains (e.g., basalt or andesite). To better constrain the role of the supraglacial ecosystems in the carbon and nitrogen cycles, to gain insight into microbiome composition and function in alpine glacial systems overriding volcanic terrains, and to constrain potential elemental sequestration or release through weathering processes associated with snow algae communities, we are aim to characterize the microbial community composition and biogeochemical cycling of snow algae communities on stratovolcanoes in the Cascade Range of the Pacific Northwest.
Microbial primary productivity in the Proterozoic oceans The delay in the rise of oxygen to present day levels at the end of the Proterozoic (~542 million years ago) represents an important gap in our understanding of ancient biogeochemical cycling. One hypothesis suggests contributions to primary production by anoxygenic phototrophs, including metabolically versatile cyanobacteria, effectively limited oxygen production throughout Earth's middle age (Johnston et al., 2009). Little Salt Spring, a karst sinkhole in Sarasota County, FL, USA, has micromolar concentrations of both oxygen and sulfide in the photic zone, conditions that may have been widespread in surface oceans during long stretches of the Proterozoic. Phototrophic pinnacle mats comprised of cyanobacteria and green sulfur bacteria occupy the sediment-water interface in the sunlit upper basin of the sinkhole. The water chemistry of the sinkhole combined with these conspicuous microbial populations provide a model analog system for determining the role of anoxygenic photosynthesis in the delay of oxygenation of the surface oceans. This work is carried out in collaboration with a number of excellent scientists - Dr. Jenn Macalady, Dr. Kate Freeman, and talented graduate student Laurence Bird at Penn State, Dr. Miriam Weber and Dr. Christian Lott at the Hydra Institute, Dr. Dirk de Beer, Dr. Anthony Dron, and Judith Klatt at the Max Planck Institute for Marine Microbiology.
Metabolically versatile Cyanobacteria Cyanobacteria are only prokaryotes that carry out oxygenic photosynthesis and therefore played a crucial role in the evolution of Earth’s atmosphere as well as diversification of microbial and higher life forms. In sunlit environments where low oxygen concentrations and sulfide persist, some Cyanobacteria can use sulfide as the electron donor to photosystem I in the absence of oxygen generation, enabling photosystem II-independent photoassimilation of CO2. Examples of well-characterized Cyanobacteria capable of anoxygenic photosynthesis are rare and the process is not well understood. Utilizing a model cyanobacterium isolated from an environment where low levels of oxygen and sulfide are present, we are characterizing the genetic, regulatory and biochemical underpinnings of anoxygenic photosynthetic activity. This work is carried out in collaboration with a number of excellent scientists - Dr. Jenn Macalady, Dr. Miriam Weber and Dr. Christian Lott at the Hydra Institute, Dr. Dirk de Beer, Dr. Anthony Dron, and Judith Klatt at the Max Planck Institute for Marine Microbiology.
Competitive Interactions and microbial community assembly Microbial processes that regulate availability of nutrients play key roles in shaping community composition. Biological nitrogen fixation, or the reduction of dinitrogen (N2) to ammonia (NH3), is a keystone process in N limited ecosystems, providing nitrogen for members of the community. N2 fixing organisms likely represent a ‘bottom up’ control on the structure of communities that develop in N limited environments. Nitrification, or the sequential oxidation of NH4+ to nitrite (NO2-) and ultimately nitrate (NO3-), can be considered a ‘top down’ control on the structure of communities that develop in N limited environments. Our research in Yellowstone National Park reveals a strong correlation between the distribution of ammonia oxidizing archaea and nitrogen fixing aquificae in nitrogen-limited geothermal hot springs over large environmental gradients. Based on the physiology of these organisms, we propose that the strong co-distributional pattern results from interspecies interactions, namely competition for bioavailable ammonia. We are employing microcosm and pure culture studies to test the hypothesis that affinity for substrate and electron donor use play key roles in structuring the biodiversity of these hydrothermal communities, and likely influences the structure of other N limited ecosystems. This research is in collaboration with Dr. Eric Boyd at Montana State University and Dr. Jose de la Torre at San Francisco State Univeristy.
The co-occurrence of cyanobacteria and anoxygenic phototrophs is common in euxinic lakes, cyanobacterial mats, hot springs, and hypersaline lagoons where sufficient fluxes of reduced compounds are available to support anoxygenic photosynthesis. However, the geochemical and biological factors controlling competition among co-existing phototrophs in natural environments is poorly understood. Using pure cultures and in situ studies, we are identifying the physical, geochemical, and physiological factors that affect competition among chlorophototrophs and consequences of this competition.
Sulfur cycling Euxinic conditions have been an intermittent feature of global oceans throughout Earth's history. Although rare today, persistently euxinic environments such as permanently stratified (meromictic) lakes serve as modern analogues to ancient water columns and their associated sedimentary basins. These stratified systems have large geochemical gradients and often host phototrophic communities at the boundary between oxic and euxinic zones (chemocline). Complex biogeochemical cycles occur throughout the water column in these systems as well as within the chemocline. We are examining the carbon and sulfur cycles within chemocline communities and the underlying anoxic water column to understand the inputs (e.g., organic carbon or oxidized sulfur) necessary to maintain these stable ecosystems.
Trace metal availability and metalloenzymes Early Earth was oxygen-poor, resulting in different bioavailability of redox sensitive trace metals than observed today. For instance, iron reacts with H2S in sulfide-rich water, forming insoluble sulfides that remove molybdenum from the water column. Throughout much of Earth's history, surface oceans experienced at least localized euxinic conditions. In contrast, iron is scarce in the modern oxygen-rich ocean whereas molybdenum, present as molybdate, is highly soluble and readily bioavailable. Because ocean redox conditions and redox-sensitive metal availability are linked, the evolution of metalloenzymes may follow a trajectory that mimics prevailing redox conditions. We are using model organisms to determine the bioavailability of metals that are complexed with sulfides and in more complex minerals to examine the links between redox conditions and the evolution of metalloenzymes.
Ecology and Physiology of toxin-producing Cyanobacteria Rising temperatures, enhanced vertical stratification, and increased eutrophication on regional and local scales has lead to increased occurrence and magnitude of blooms of harmful cyanobacteria in freshwater ecosystems. We aim to contribute to the development of empirically based strategies to protect freshwater ecosystems from harmful cyanobacterial blooms by determining physiochemical parameters that select for the specific cyanobacterial species that drive bloom formation and how these parameters affect toxin production.