Systems Geobiology: CaCO3-Water-Microbe Feedback Interactions in Hot Springs and Coral Reef Ecosystems

Bruce W. Fouke, University of Illinois Urbana-Champaign

Department of Geology, Department of Microbiology, and Institute for Genomic Biology

Systems Geobiology Overview
A fundamental shift is underway in the geosciences in response to the recognition that microorganisms play a fundamental role in the co-evolution of our planet and biosphere. This realization has been shaped by the application of DNA biotechnology to a wide variety of geological marine and terrestrial environments around the world. These studies have revealed that microorganisms drive key global chemical cycles, comprise over half of all living cellular organic carbon (>1030microbial cells inhabit the planet) and contain the overwhelming majority of genetic diversity. As a result, natural scientists are now probing one of the foremost theoretical and practical scientific questions of our time: How have Microbial Life and Earth coevolved through geological time and what will future co-evolution yield in the face of ongoing global environmental change? Systems Geobiology is the name given to this emerging field at the intersection of the geological, chemical, physical and life sciences.

Systems Geobiology Research
The Fouke lab at Illinois has undertaken a decade of coordinated Systems Geobiology research on Yellowstone hot springs and Caribbean and Pacific coral reef ecosystems. While at first glance these seem like wildly different and unrelated environments, closer examination indicates a host of striking similarities and scientific parallels. The spring water at Mammoth Hot Springs in northern Yellowstone is derived from rain and snowmelt runoff in the Gallatin Mountains that flows down along faults into the rock subsurface. This groundwater is then heated by the Yellowstone supervolcano to ~100oC (212oF), chemically dissolves deeply buried ~350 million year old marine limestone, and flows back up to the surface to emerge from vents at a temperature of 73oC (163oF). During this hydrologic journey, the Mammoth Hot Spring water evolves a salty chemical composition remarkably similar to that of seawater. Furthermore, the limestone rock (called travertine) that precipitates to form the classic meter-scale terraced steps of Mammoth Hot Springs are composed of a form of calcium carbonate (CaCO3) mineral called aragonite. This is the same mineral that corals use to precipitate and grow their skeletons. In addition, several of the microbes that we have identified in the 73 to 25oC (163 – 77oF) hot-spring vent drainage patterns at Yellowstone are similar, and sometimes identical, to the microbes inhabiting coral tissues, coral mucus and seawater.

As a result, our field-based controlled experiments at Yellowstone are now being used to predict how corals will respond to future global warming. Heat-loving (thermophilic) microbes living at 65 to 71oC in Yellowstone are able to respond to shifts in water flow rate and temperature by changing the speed at which travertine rock (aragonite) is deposited on the floor of the drainage channels. Our biochemical analyses suggest that the microbes do this by producing different types of protein under different water temperature and flow conditions. We are now applying this mechanism derived from Yellowstone to form new interpretations of how density banding in the aragonitic skeleton of scleractinian corals (similar to tree rings) reflects coral response to changing sea surface temperature. Accurate interpretation of coral skeleton density banding is critically important for predicting future changes in sea surface temperature and thus plays a central role in shaping long-term policy strategies on global warming.

Systems Geobiology Teaching
I teach a variety of courses at Illinois that emphasize the role of microbes in key earth system process. The students in these courses are from many different disciplines, including geology, microbiology, physics, chemistry, engineering, and animal sciences. These courses, have a significant lab component and a field trip, include GEOL 143 History of Life (162 students every Fall), GEOL Sedimentology and Stratigraphy (30 students every Spring), GEOL 415/515 Modern-Ancient Coral Reef Geobiology (SCUBA-based with 30 students every other Spring), and CHP 392 Yellowstone Biocomplexity (30 students every other Fall). I am now including a genomic/metagenomic component in all of these courses, each illustrating the quantitative and qualitative linkages of microbial molecular ecology (and resulting knowledge of community composition and metabolic activity) with understanding of the physical, chemical and biological structure of a natural environment across multidimensional scales of time and space.

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