USC College of Letters & Sciences

Education

Postdoctoral Training

Description of Research

Summary Statement of Research Interests

I am a microbial ecologist principally interested in deep-sea hydrothermal systems and the prokaryotic life they harbor. I use biogeochemical analyses, traditional microbiological techniques, and molecular biology approaches to better understand what microbes live in hydrothermally influenced systems and how and why they are different from the water column microbes in the surrounding ocean water. I also study carbon (C), nitrogen (N) and phosphorus (P) cycling in marine systems, including both water column and hydrothermally influenced systems. Below are outlined the themes of my current research.

What is the endemic microbial population in hydrothermal plumes? My work and that of others before me indicates that there is a unique microbial population specifically within hydrothermal plumes that is different from that in direct (undiluted) hydrothermal fluids, the source of hydrothermal plumes, and the deep ocean water surrounding the plumes. I aim to characterize this population and quantify its biogeochemical impact in the ocean by analyzing samples in rising (non-buoyant) and neutrally buoyant hydrothermal plumes for N, P and silica (Si) chemistry and microbial community structure as assessed by analysis of the 16S rRNA gene. The two aims of this research are to 1) understand how the microbial population changes as hydrothermal plumes are diluted in the water column with deep ocean water over distance scales from meters to kilometers, and 2) to assess what role chemistry plays in recruiting and maintaining this unique population.

What are microbial metabolic rates on and in deep ocean basalts? Little is known about the metabolic rates of microbes living on and in deep ocean basalts. Given that basalt represents the largest continuously inhabitable substrate on Earth, these microbes likely have significant impacts on global carbon cycling. Using incubation experiments, I am interested in quantifying the rate of metabolism of endolithic microbes on seafloor and subseafloor basalts. Currently, I am using 13C-labelled bicarbonate to assess autotrophic production in seafloor basalts as well as fluorescently labeled enzyme substrates to analyze C, N and P utilization in these same rocks. Molecular analysis of microbial community structure will be carried out to attempt to pinpoint the microbes responsible for the metabolic activity measured using proven methods such as clone library construction of 16S rRNA to analyze microbial community composition.

What controls microbial biogeography? Dominant microbial populations in marine systems exhibit distributions that are distinct, despite relatively few limits to dispersal mechanisms in the ocean. I am interested in understanding what drives the observed biogeographical patterns, both in surface water organisms, such as the cyanobacterium Synechococcus, as well as in hydrothermal ecosystems. To do so, I use a variety of techniques including analysis of functional genes, community fingerprinting methods, and employing statistical analyses of molecular data.

Biogeochemical cycling of nutrients. My current work is focused on hydrothermal ecosystems, but my graduate training was in nutrient (C, N, P and Si) cycling in the upper water column. I have applied this interest to deep ocean sites, such as the Loihi Seamount, where I am studying C, N, P and Si chemistry in hydrothermal fluids and plumes. Questions of nutrient limitation in general and also its role in possible mitigation of coastal eutrophication remain of interest to me as well.