Investigation of Protists in the Deep Marine Subsurface Biosphere


DOEI Funded Research: 2008

Proposal Summary

What are the primary questions you are trying to address with this research? (Or, if more appropriate, is there a hypothesis or theory that you are trying to prove or disprove?)
We are examining the question of whether or not single celled eukaryotic organisms (protists) are present and active in the deep marine subsurface. Archaeal communities in the deep subsurface were shown to be heterotropic. If protists represent the next trophic level, they will most likely also be heterotrophic, and their numbers will depend on prey cell density.

What is the significance of this research for others working in this field of inquiry and for the broader scientific community?
Marine sediments cover more than two thirds of the Earth’s surface. Bacteria and Archaea of the deep subsurface have been estimated to constitute as much as one-third of Earth’s total living biomass and their activities catalyze the biogeochemical recycling of buried organic matter. Despite this, relatively little is known about this deep subsurface biosphere, and essentially nothing is known about the presence of protists in sediments deeper than a few cm. Through grazing pressure, protists may alter bacterial and archaeal community composition and have impacts on microbial net production and nutrient cycling.

What is the significance of this research for society?
Studies of the microbiota of the deep marine biosphere will lead to a greater understanding of Earth processes, particularly marine biogeochemical cycles.

When and where will this investigation be conducted? (For instance, is this new fieldwork, or a new analysis of existing data?)
This project will not require new fieldwork. We will analyze four deep subsurface cores collected by Andreas Teske (UNC, Chapel Hill) from sites representing a spectrum of organic carbon content. 

What are the key tools or instruments needed to conduct this research?
While the groundwork for RNA extraction methods for these deep subsurface sediments has been laid by the Teske laboratory (UNC, Chapel Hill), the presence of eukaryotes in the deep subsurface has not been investigated. This DOEI project will 1) determine if microbial eukaryotes are present in these samples, 2) will provide an initial diversity assessment if they exist, and 3) will refine the RNA extraction protocols using samples from four deep subsurface cores (provided by Teske).

What are the greatest challenges – physical or intellectual – to conducting this investigation?
The greatest challenge is developing RNA extraction protocols that will work for marine sediment samples with a wide range of chemical characteristics. While the groundwork for these methods has been laid by the Teske laboratory (UNC, Chapel Hill), this project will refine these protocols using samples from four deep subsurface cores (provided by Teske).

Is this research part of a larger project or program?
If eukaryotes are present, these data will then form an essential foundation for a larger proposal to either NSF ODP, NSF MIP or NSF Biotic Surveys to perform a broad-scale investigation into the ecology of deep subsurface eukaryotes from a much wider selection of organic-poor and organic-rich sample sites from around the world.

If you have conducted previous/similar work on this subject, please suggest any web links or citations that might help others better understand the background to your line of research.
We have not looked for microbial eukaryotes in the deep subsurface (no one has), but we have studied surficial marine sediment microbial communities.  Figure 1 from Edgcomb et al. 2002 shows the breadth of diversity present in the near surface of a hydrothermal vent site. 

Edgcomb, VP, DT Kysela, A Teske, ADV Gomez, ML Sogin. 2002. Benthic eukaryotic diversity in the Guaymas Basin hydrothermal vent environment. PNAS 99(11):7663-7668. 

Teske, A., K.-U. Hinrichs, V. Edgcomb, A. d.V. Gomez, D. Kysela, M.L. Sogin, and H.W. Jannasch 2002. Archaeal and bacterial population structure of hydrothermal sediments at the Guaymas Basin vent sites: evidence for anaerobic methanotrophy. Applied and Environmental Microbiology 68(4):1994-2007. 

Edgcomb, V.P., J.M. Bernhard, and S. Jeon. 2007. Deep-sea microbial eukaryotes in anoxic, microoxic, and sulfidic environments, In: J. Seckbach (ed.) Algae and Cyanobacteria in Extreme Environments. Vol. 11, Springer-Verlag. 

Shimeta, J., Gast, R.J. and J.M. Rose. 2007. Community structure of marine sedimentary protists in relation to flow and grain size. Aquatic Microbial Ecology 48:91-104. 

Please provide some biographical information, such as place of birth, degrees earned, significant awards or honors, research interests, reasons why you became a scientist or why you are interested in this line of research, and any personal interests, hobbies, or details that you are willing to share.
Edgcomb:  Born Morristown, NJ, PhD from University of Delaware 1997. 

NASA/NRC Astrobiology Institute Postdoctoral Associateship, 2000 and 2001. 

I spent a lot of time in the outdoors from an early age, particularly around the ocean, and developed a natural curiosity about the cycles of nature and an appreciation for biodiversity of all types. When I learned in college about the fundamental importance of microbes to Earth’s major biogeochemical cycles I knew I wanted to understand more about how these unseen communities worked together to achieve their important functions, and to make whatever contribution I could to preserving biodiversity through increasing our knowledge of it.  My particular interest in protist diversity came from my incredible experiences as a postdoc under Mitchell Sogin at the Marine Biological Laboratory, who made many training/education opportunities possible for me in this area.

Current hobbies? Sea kayaking, birding, hiking, gardening, and martial arts.

Gast:  Born Cleveland, OH.  PhD from The Ohio State University 1994.

In my sophomore year of college, I took a general microbiology class and have been fascinated by microbes ever since, especially protists.  My work investigates many different aspects of protistan biology, but I would say what fascinates me the most is the ability of protists to adapt to life in a wide variety of environments, like the Southern Ocean of the Antarctic, or symbiotic and parasitic states.