Microbial Ecology and Energetics in Yellowstone Hot Springs

14(1) • Winter 2006 Yellowstone Science ANY ECOSYSTEM on Earth is comprised of all living things (plants, animals, etc.) and non-living things (rocks, soil, water, etc.) in a given geographic area. That area can be on the scale of a landscape, such as the Greater Yellowstone Ecosystem (GYE, multiple states in size), to the local area around a single hot spring, to the area within some minute distance between bacteria. There is a constant exchange of materials between the living and non-living components in any of these ecosystems. One of the most important of these exchanged materials is energy. When we walk around the GYE, the energy source for the richness of life we can see is apparent: photosynthesis, the capture of light energy from the sun into usable form. This capture is made possible by the fixation of the sun’s photons into useful chemical energy by plant cell chloroplasts. The living components of an ecosystem are composed of a blend of organisms we now know to occupy three domains of life. In the first of these three domains, members of Eucarya make up most of the world we see, including plants, animals, and fungi. Members of the other two domains, Bacteria and Archaea, are all microbial, and perform many ecosystem services, such as primary productivity, waste recycling, weathering, and mineralization. Microbial capture of the sun’s energy by photosynthesis is conducted by algae, a group of microbial organisms within the domain Eucarya, and cyanobacteria, a group of organisms within the domain Bacteria. Components of the third domain of life, Archaea, are not known to engage in traditional photosynthesis at this time. Once photosynthesis converts light energy into biomass, many other organisms, including animals, then thrive by consuming this energy. Photosynthesis thus provides the energy foundation for our macrobial-visible, eukaryotic world. Photosynthesis by bacteria is visible all over Yellowstone, in the form of the many colors in and around hot springs (Figure 1). A walk around the park reveals a multitude of colorful microbial mats (whole assemblages of microorganisms) living at various temperatures and pHs under different site-dependent chemical regimes. These colors are often the product of photosynthetic pigments within the microbial cells. The green, black, orange, brown, and yellow mats around Grand Prismatic Spring, or around the boardwalks of the Lower Geyser Basin, are examples of photosynthetic mats. These microbial mats form their own complex ecosystems, composed of mixed communities of microorganisms living together with a few Microbial Ecology and Energetics in Yellowstone Hot Springs