One of the prominent goals of astrobiology is to discover life or signs of life on planets beyond Earth. To approach this goal, it will be useful to know the physical and chemical limits for life on Earth and, perhaps more importantly, to understand the underlying biophysical characteristics of life that set these limits. Such knowledge would allow us to make educated guesses- based on remote measurements of physical and chemical parameters alone- about the likelihood of finding life on other planets.

Although an inventory of life on Earth is far from complete, it is clear that microbes dominate most habitats, especially extreme habitats. The term "extremophiles" is the name given to the organisms (mostly bacteria and archaea) living in places that are physically and chemically extreme, that is extreme from our human perspective. Such habitats include the boiling mud of geothermal hot springs and super-heated waters of submarine hydrothermal vents, the frozen soils of Siberia and the sea-ice of the arctic, the 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. The extremophiles are specifically adapted to these habitats, however, and they in turn would be killed or incapacitated in the habitats we consider hospitable. For example, the extremophiles known as "thermophiles," which live in hot springs (>50¡C), are metabolically "frozen" when they are cooled to what we consider a comfortable temperature. The extremophiles known as "psychrophiles" which grow at temperatures down to Ð20¡C, are "cooked" at this same "comfortable" temperature. The extremophiles known as "barophiles," which live at the bottom of the deepest parts of the ocean at >1,000-atmospheres pressure, die rapidly when they are decompressed to one atmosphere. The extremophiles known as "halophiles" which live in waters saturated with salts, burst in fresh water; while "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 the extremophiles represent the ingenuity and versatility of evolution to exploit an appropriate energy source and adapt to what appear to be harsh conditions.

Our knowledge of extremophiles on Earth continues to expand as we explore the more remote and seemingly inhospitable environments using advanced technologies. Molecular probes, for example, 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 are not only providing tools for discovering the more extreme extremophiles, they are providing tools for understanding the molecular basis for their existence. In return the extremophiles are providing macromolecules and inspiration for addressing fundamental questions in biology, biotechnology, and nanotechnology.

The extremophile research group at Ames is focused on three fundamental questions:
1. What are the physical and chemical limits to which life has adapted on Earth?
2. What are the molecular adaptations that have allowed living systems to inhabit extreme environments?
3. How can we apply what we learn from extremophiles to important problems in biotechnology, nanotechnology, and planetary protection?

To address the first question and to expand our understanding of the physical and chemical limits for life on Earth we are exploring geothermal areas in Yellowstone and most recently 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 the most extreme conditions. To address the second question concerning the molecular adaptations of extremophiles, we are studying 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 and we have discovered that this protein is closely related to a human protein of previously unknown function. Our studies have provided insights into the function of this protein and 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 concerning how we can apply what we learn from extremophiles, we are studying 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. For example, we are studying the most radiation resistant organism known, Deinococcus radiodurans, to find its "Achilles heel" and 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 used by biotechnologists and future nanotechnologists, technologists who may be critical for future NASA missions.

NASA's efforts to optimize space exploration are obviously enhanced by developments that create smaller and more powerful sensors and information storage devices. Such devices, which depend on the controlled organization of materials into addressable arrays, are currently fabricated primarily by lithographic techniques. While these techniques have been refined to create devices on the micron scale, there are compelling reasons to produce nanoscale devices. In addition to the increased packing density, on the nanoscale there are unique effects that arise from quantum confinement. These quantum effects may open new horizons in electronics technologies, which explains the growing excitement about nanotechnology.

Controlled assembly of materials on the nanometer scale, however, presents a formidable problem. It is beyond the theoretical and practical limits of conventional lithographic patterning processes and while alternate techniques, such as X-ray and particle beam lithography have the resolution to reach the nanoscale, they are currently prohibitively expensive and laborious procedures. We are developing alternative new techniques for patterning materials on the nanoscale using self-assembling proteins.

Proteins are biomolecules that can naturally form highly order structures and most importantly can be modified and manipulated by genetic engineering. Genetic engineering transforms natural proteins into designer 'nano-agents' that are capable of recognizing, binding, and ordering nanoscale materials.

We have demonstrated the feasibility of using proteins as nano-agents with a class of proteins called HSP60s. These proteins naturally associate to form rings 17 nanometers in diameter called chaperonins. Chaperonins can be induced to form higher order structures such as chains or two- and three- dimensional crystals. By genetically engineering HSP60s to bind metal or semiconductor materials, chaperonins can create useful nanoscale devices such as wires, wave-guides, and quantum dot arrays. We have demonstrated, for example, that two-dimensional crystals of chaperonins can produce two-dimensional arrays of quantum dots (Fig. 1 and 2 from Nature Materials paper). The properties of these arrays and the construction of other structures using chaperonins are currently under investigation.

Advances in Genomics, Proteomics, and Structural Genomics have refined our knowledge of proteins on the nanoscale. This knowledge combined with techniques in genetic engineering represents a formidable tool for nanotechnology. NASA is helping to explore the frontiers of bio-nanotechnology and it remains to be seen how this will impact future NASA missions.