THERMOPHILES Thermophiles, or heat-loving microscopic organisms, are nourished by the extreme habitat at hydrothermal features in Yellowstone National Park. They also color hydrothermal features shown here at Clepsydra Geyser. Life in Extreme Heat The hydrothermal features of Yellowstone are enough to blister your skin. Some create layers that magnificent evidence of Earth’s volcanic activity. look like molten wax on the surface of steaming Amazingly, they are also habitats in which micro- alkaline pools. Still others, apparent to us through scopic organisms called thermophiles—“thermo” for the odors they create, exist only in murky, sulfuric heat, “phile” for lover—survive and thrive. caldrons that stink worse than rotten eggs. Grand Prismatic Spring at Midway Geyser Basin Today, many scientists study Yellowstone’s ther- is an outstanding example of this dual characteristic. mophiles. Some of these microbes are similar to the Visitors marvel at its size and brilliant colors. The boardwalk crosses a vast habitat for thermophiles. Nourished by energy and chemical building blocks Words to Know available in the hot springs, microbes construct Extremophile: A microorganism living in extreme vividly colored communities. Living with these conditions such as heat and acid, that cannot survive without these conditions. microscopic life forms are larger examples of life in extreme environments, such as mites, flies, spiders, Thermophile: Heat-loving extremophile. and plants. Microorganism: Single- or multi-celled organism of microscopic or submicroscopic size. Also called a microbe. For thousands of years, people have likely won- dered about these extreme habitats. The color of Microbes in Yellowstone: In addition to the thermophilic microorganisms, millions of other microbes thrive in Yellowstone’s superheated environments certainly Yellowstone’s soils, streams, rivers, lakes, vegetation, and caused geologist Walter Harvey Weed to pause, think, animals. Some of them are discussed in other chapters of and even question scientists who preceded him. In this book. 1889, he wrote: Bacteria (Bacterium): Single-celled microorganisms There is good reason to believe that the existence without nuclei, varying in shape, metabolism, and ability to move. of algae of other colors, particularly the pink, yel- Archaea (Archaeum): Single-celled microorganisms low and red forms so common in the Yellowstone without nuclei and with membranes different from all waters, have been overlooked or mistaken for other organisms. Once thought to be bacteria. deposits of purely mineral matter. Viruses: Non-living parasitic microorganisms consisting of However, he could not have imagined what a a piece of DNA or RNA coated by protein. fantastic world exists in these waters of brimstone. Eukarya (Eukaryote): Single- or multi-celled organisms Species, unseen to the human eye, thrive in waters whose cells contain a distinct membrane-bound nucleus. as acidic as the liquid in your car battery and hot Life in Extreme Heat 131 th Thermophiles in the Tree of Life THERMOPHILES Bacteria Archaea Eukarya Green nonsulfur Crenarchaeota Myxomycota bacteria Euryarchaeota Entamoebae Animalia Mitochondrian Fungi Gram- positive Thaumarchaeota Proteobacteria bacteria Plantae Chloroblast Ciliates Cyanobacteria Korarchaeota Nanoarchaeota Flavobacteria Flagellates Thermotoga Trichomonads Thermodesulfobacterium Microsporidia Aquifex Diplomonads DRAWING BY MARY ANN FRANKE Yellowstone’s hot springs contain branch of microorganisms not known Relevance to Yellowstone species from the circled groups on this until the 1970s—the Archaea. Among the earliest organisms to Tree of Life. Jack Farmer conceived of evolve on Earth were microorganisms Dr. Carl Woese first proposed this this version of the tree of life, which first whose descendants are found today “tree” in the 1970s. He also proposed appeared in GSA Today, July 2000 (used in extreme high-temperature, and in the new branch, Archaea, which with permission). some cases acidic, environments, such includes many microorganisms formerly as those in Yellowstone. Their history In the last few decades, microbial considered bacteria. The red line links exhibits principles of ecology and ways research has led to a revised tree of the earliest organisms that evolved in which geologic processes might have life, far different from the one taught from a common ancestor. These are influenced biological evolution. before. The new tree combines animal, all hyperthermophiles, which thrive in plant, and fungi in one branch. The water above 176°F (80°C), indicating other two branches consist solely of life may have arisen in hot environments microorganisms, including an entire on the young Earth. first life forms capable of photosynthesis—the process Regardless of scientific advances, visitors and of using sunlight to convert water and carbon dioxide explorers in Yellowstone can still relate to something to oxygen, sugars, and other by-products. These life else Weed wrote about Yellowstone, more than a forms, called cyanobacteria, began to create an at- century ago: mosphere that would eventually support human life. The vegetation of the acid waters is seldom a Cyanobacteria are found in some of the colorful mats conspicuous feature of the springs. But in the and streamers of Yellowstone’s hot springs. alkaline waters that characterize the geyser basins, and in the carbonated, calcareous waters About Microbes of the Mammoth Hot Springs, the case is other- Other life forms—the Archaea—predated cyanobac- wise, and the red and yellow tinges of the algae teria and other photosynthesizers. Archaea can live combine with the weird whiteness of the sinter in the hottest, most acidic conditions in Yellowstone; and the varied blue and green of the hot water their relatives are considered among the very earliest to form a scene that is, without doubt, one of life forms on Earth. the most beautiful as well as one of the strangest Yellowstone’s thermophiles and their environments sights in the world. provide a living laboratory for scientists, who continue to explore these extraordinary organisms. Researchers know that many mysteries of Yellowstone’s extreme environments remain to be revealed. 132 Yellowstone Resources and Issues Handbook, 2019 THERMOPHILES thermoacidophilic eukaryotic alga. Proceedings of the More Information National Academy of Sciences of the United States of American Society for Microbiology: www.microbeworld.org America. 106 (13): 5213. Allen, E. T., Arthur L. Day, and H.E. Merwin. 1935. Hot Reysenbach, A.L., and Shock, E. L. 2002 . Merging Genomes springs of the Yellowstone National Park. [Washington]: with Geochemistry in Hydrothermal Ecosystems. Carnegie institution of Washington. Science. 296: 1077-1082. Brock, T.D. 1994. Life at High Temperatures. Yellowstone Sheehan, K.B. et al. 2005. Seen and unseen: discovering the Association/Mammoth, WY. microbes of Yellowstone. Guilford, Conn: Falcon. Brock, Thomas D. 1995. The road to Yellowstone and be- Snyder, J.C. et. al. 2013. Functional interplay between a yond. Annual Review of Microbiology. 49 virus and the ESCRT machinery in Archaea. Proceedings Dyer, B.D. 2003. A field guide to bacteria. Ithaca, NY: of the National Academy of Sciences. 110 (26) Cornell University Press. 10783-10787. Franke, M.A, et. al. 2013. Genetic Diversity in Yellowstone Spear, J. R. et. al. 2005. Hydrogen and bioenergetics in the Lake: The Hot and Cold Spots. Yellowstone Science 21 Yellowstone geothermal ecosystem. Proceedings of the (1): 6-22. National Academy of Sciences. 102 (7) 2555-2560. Fouke. B.W. 2011 . Hot-spring Systems Geobiology: abi- Steunou A.S., et. al. 2008. Regulation of nif gene expression otic and biotic influences on travertine formation at and the energetics of N2 fixation over the diel cycle in a Mammoth Hot Springs, Yellowstone National Park, hot spring microbial mat. ISME Journal. (4):364-78. USA. Sedimentology. 58: 170-219. Takacs-Vesbach, C., et al. 2013. Metagenome sequence Hamilton, T.L. et. al. 2012. Environmental constraints defin- analysis of filamentous microbial communities obtained ing the distribution, composition, and evolution of from geochemically distinct geothermal channels reveals chlorophototrophs in thermal features of Yellowstone specialization of three aquificales lineages. Frontiers National Park. Geobiology. (10) 3: 236-249. Research Foundation. Inskeep WP , et. al. 2013. The YNP metagenome project: Thermal Biology Institute of Montana State University: www. environmental parameters responsible for microbial tbi.montana.edu distribution in Yellowstone. Frontiers in Microbiology. Ward, D.M., Castenholz, D.W., and Miller, S.R. 2012. 00067. Cyanobacteria in Geothermal Habitats. In Brian A. Klatt, C. G., et. al. 2011. Community ecology of hot spring Whitton, ed. Ecology of cyanobacteria II: their diversity cyanobacterial mats: predominant populations and their in space and time. Dordrecht: Springer functional potential. ISME Journal. 5(8): 1262–1278. Marquez, Luis et al. 2007. A virus in a fungus in a plant: Reviewers 3-way symbiosis required for thermal tolerance. Science Dr. Eric Boyd, Montana State University Department of 315 (5811): 513–515. Microbiology and Immunology Qin, J., C.R. Lehr, C. Yuan, X. C. Le, T. R. McDermott, and B. Annie Carlson, Research Permit Coordinator P. Rosen. Biotransformation of arsenic by a Yellowstone Life in Extreme Heat 133 THERMOPHILES The travertine terraces in Mammoth Hot Springs host thermophilic cyanobacteria. Thermophilic Bacteria sulfur,