USC Dana and David Dornsife College of Letters, Arts and Sciences

Education

Postdoctoral Training

Description of Research

Summary Statement of Research Interests

Microbes are the major mediators of biogeochemical cycles on earth. Initial work indicates that a potentially high biomass and active microbial biosphere exists in the subseafloor ocean crust that lies below seafloor sediments, but data is currently limited to a few sites and studies. Likewise, seafloor exposed ocean crust at mid-ocean ridges, inactive hydrothermal sulfides and hydrothermal plumes are also globally distributed microbial substrates that host a potentially large biomass. For all these habitats, the magnitude and diversity of the microbial community and rates of biogeochemical transformations are currently unconstrained. I utilize biogeochemical analyses, traditional microbiological techniques, mineralogy, geochemistry and and molecular biology to better understand:

1. what is the biomass of the ocean crust?
2. what microbes live in these globally distributed deep ocean environments?
3. how does substrate chemistry drive microbial population structure?
4. What impact does the microbial community have on both the degradation of these rock habitats, and more broadly, marine biogeochemistry?

Below are outlined the themes of my current research.

What is the biomass of the ocean crust? I am currently employing cutting edge techniques of biomass enumeration, combining cell separation from rocks and subsequent flow cytometry with deep-UV native fluorescence, to quantify the microbial biomass in subseafloor ocean crust samples I collected as the only microbiologist during Integrated Ocean Drilling Program Expedition 330 to the Louisville Seamount Chain (LSC). This is important, as no quantitative numbers for microbial biomass in subseafloor ocean crust currently exist. I aim to expand this work to additional sites and to create a global model of subseafloor microbial biomass in ocean crust.

What microbes live in these globally distributed deep ocean environments ? Microbial diversity in deep ocean environments is poorly understood, especially in relation to temporal scales. I currently focus on describing the microbial diversity of hydrothermal vent plumes, inactive hydrothermal sulfides and the ocean crust, although I am open to expanding my focus in the future. My overall goal is to understand the role microbes in these settings have on marine biogeochemistry.

How does substrate chemistry drive microbial population structure ? Substrate chemistry can control what microbes survive in a given environment, but exactly how important it is at and below the seafloor is not well constrained. I am especially interested in how substrate chemistry drives microbial population structure on seafloor basalts and inactive hydrothermal sulfide chimneys. I seek to understand the temporal scale over which this changes in microbial populations occur as these rocks age, from decades to millennia.

What impact does the microbial community have on both the degradation of these rock habitats, and more broadly, marine biogeochemistry ? Basalt represents the largest continuously inhabitable substrate on Earth, therefore the microbes living on and in seafloor and subseafloor basalt likely have significant impacts on global biogeochemistry. Despite their potential impact, little is known about the metabolic rates of these microbes. I utilize stable isotope labelled incubation experiments coupled with molecular biology and NanoSIMS to quantify autotrophic production on seafloor rocks, identify the organisms involved and visualize the incorporation of labeled bicarbonate on a single cell level. My goal is to gain a better understanding of autotrophic production and biogeochemical cycling on inactive sulfide chimneys as well as ocean crust samples.