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Limits of Life

Nathalie CabrolDavid DeamerChris McKayJonathan TrentDavid FikeAndrew Hock

Co-Leads: Nathalie Cabrol, David Deamer (UCSC), Chris McKay, Jonathan Trent
Research Associates: David Fike (M.I.T.), Andrew Hock (UCLA), both Academy Alumni

• Life's Extremes & Life's Origins
• Field Trip to a Remote Site
• Group Project

This summer research team focuses on Goal 5 of the Astrobiology Roadmap - searching for the limits of life on Earth.

The term “extremophiles” is the name given to the organisms (mostly bacteria and archaea) living in places that are physically and chemically extreme (from our human perspective). Their habitats include boiling mud of geothermal hot springs, super-heated waters of submarine hydrothermal vents, frozen soils of Siberia, sea-ice of the arctic, extremely high pressures at the bottom of the deepest parts of the oceans, and a variety of places where the local chemistry would be instantly toxic to human beings. Extremophiles are adapted to these habitats, and would die in habitats that we find hospitable.

1. Chris McKay at an ice hole, Antarctica. 2. Jonathan Trent on an Astrobiology expedition to Kamchatka, Siberia. Inside the Mutnovski caldera. 3. Nathalie Cabrol at the summit of the volcano Licanbur in the Bolivian Andes, where an astrobiology team did field work, finding extremophiles at Laguna Verde (the highest lake in the world). 4. Underwater diving training at Lassen (2500 m).

Extremophiles known as thermophiles live in hot springs (>50°C); they are metabolically “frozen” when they are cooled to what we consider a comfortable temperature. Extremophiles known as psychrophiles grow at temperatures below 20°C and are able to grow at 0°C; they are “cooked” at our body temperature (37°C). Extremophiles known as piezophiles or barophiles live at the bottom of the deepest parts of the ocean at >1,000 atmospheres pressure; they die rapidly when decompressed to one atmosphere. Extremophiles known as halophiles live in waters saturated with salts; they burst in fresh water. Acidophiles thrive in concentrated acid (pH 0.5) and are destroyed at neutral pH. Other extremophiles are specifically adapted to live in areas with high levels of radiation, concentrated toxic chemicals, a paucity of nutrients, or a scarcity of water. Taken together, extremophiles represent the ingenuity and versatility of evolution to exploit energy sources and adapt to harsh conditions.

Our knowledge of extremophiles on Earth continues to expand as we explore more remote and seemingly inhospitable environments using advanced technologies. Molecular probes have revealed that conventional microbiological methods provide us with information about <1% of the diversity of organisms in most habitats; i.e. over 99% of the organisms have yet to be described and characterized. Molecular techniques and advances in microscopy and sampling procedures provide tools to discover the more extreme extremophiles and to understand the molecular basis of their existence. In return, extremophiles provide macromolecules and inspiration to address fundamental questions in biology, biotechnology, and nanotechnology, such as
  • What are the physical and chemical limits of life on Earth?
  • What molecular adaptations allow living systems to inhabit extreme environments?
  • How can we apply what we learn from extremophiles to important problems in biotechnology, nanotechnology, and planetary protection?
To address the first question about the physical and chemical limits for life on Earth we explore geothermal areas in Yellowstone and Lassen Volcanic National Park. We have developed video cameras that can be lowered into boiling hot springs with probes that allow us to profile these habitats for temperature, pH, oxygen, and depth. One goal is to discover thermoultima amesei (the highest temperature organism on Earth) and in the process to develop tools for detecting life under extreme conditions.

To address the second question about the molecular adaptations of extremophiles, we study proteins produced by an organism isolated from near-boiling sulfuric acid hot springs in Beppu, Japan. When this organism is exposed to the highest temperatures it can tolerate, it produces large amounts of a particular type of protein; we have discovered that this protein is closely related to a human protein of previously unknown function. Our studies provide insights into the function of this protein. So what began as an investigation of a protein in an esoteric extremophile has developed into a study of a protein involved in human immune responses, auto-immune diseases, arthritis, and diabetes.

Finally, to address the third question about how we can apply what we learn from extremophiles, we study how thermostable proteins can be used to stabilize and preserve other macromolecules, how a tube-forming protein can be used in nanotechnology, and how some of the most robust extremophiles could impact planetary protection. So the “Achilles heel” of the most radiation-resistant organism known, Deinococcus radiodurans may provide standards for space-craft sterilization. The existence of extremophiles is testimony to the ingenuity of evolution and the adaptability of life on Earth. For NASA the existence of extremophiles represents a challenge for planetary protection and a cause for optimism in the search for life beyond Earth. Each discovery of an extremophile that expands the physical and chemical limits for life on Earth expands the possibilities of finding life-as-we-know-it in worlds beyond Earth. These discoveries also enlarge our tool-box of macromolecules and biological processes for use by biotechnologists and future nanotechnologists, which may be critical for future NASA missions.

Five or more Research Associates will be chosen for their potential to contribute to the team effort, which aims to produce publishable results in a ten week period. The team will consist of people with appropriate skill sets for each of the extreme environments to be visited. For example, in preparation for a search for the upper temperature limit for life, the team may consist of microbiologist(s), geologist/ geochemist(s), molecular biologist(s), computational biologist(s), and videographer(s).
  • Geologists/geochemists will identify potential field sites and help to sample and characterize critical features for isolating microbes from these sites.
  • Microbiologists will isolate and characterize microbes, designing media and cultivation conditions.
  • Molecular biologists will develop field methods to determine if there is any life in the field sites of choice, using established or new methods and characterizing isolates from the microbiologists.
  • Computational biologists will determine if the data produced by the molecular biologists and microbiologists represent new species.
  • Videographers will create an educational documentary of the course, expedition, and results to be shared with the rest of the Academy and possibly used for educational outreach.
Science Goals and Deliverables
This NASA U search for the "limits of life" module has both a well defined Astrobiology science goal and an specific learning goal. The astrobiology science goal is to address the important roadmap issue of identifying the physical and chemical extremes to which life on Earth has adapted. Each year the module will focus on a specific environmental factor or combination of factors, (such as high or low temperature, high or low pH, or high or low pressures, etc.). Each year's efforts will contribute to the development of a multi-dimensional "map" that defines the limits of the biosphere. The scientific goal of the module will be to define and expand this map.

The learning goal is to provide Research Associates (RAs) with a learning experience as part of a team effort. RAs will be responsible for specific aspects of the research project; the success of the project will depend on the team effort. The project will be the basis for developing skills in information gathering, knowledge sharing, and creative thinking, as well as learning experimental techniques and data analyses.

The inclusion of videographers to document the team process is also an essential part of the science and Academy aspect of this module. The video documentary will be used for review and learning purposes for the scientists. It will also be a learning experience for the videographers, who will hone their skills through producing a documentary under demanding conditions. The video will be archived by NASA U as part of NASA Astrobiology outreach.


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