Annette Summers Engel
Donald and Florence Jones Professor of Aqueous Geochemistry
University of Tennessee at Knoxville
Department of Earth and Planetary Sciences
El Tatio in Northern Chile is located at 4440 m in the hyper-arid Atacama Desert and comprises one of the largest geyser zones known. This unique location is also a natural source of toxic metalloids (As and Sb) that locally impact regional water quality, water policy, and agricultural commerce. The waters also support isolated communities of mat-forming thermophilic microorganisms that survive in a geochemical environment of rapidly precipitating siliceous sinter with periods of extreme desiccation between geyser inundation, extreme temperatures and temperature variations, and intense solar radiation due to the high altitude low-latitude location. We measure metal-coordination, speciation, and oxidation/reduction states of As, Sb, and Fe using XANES and EXAFS , ATR-FTIR, and fluorescence spectroscopy, as well as characterize the microbial communities and functional genes. 
As(V) is the predominate oxidation state in the mats and sediment, sorbed as an inner-sphere complex to organic matter and ferric oxides, and in the mats is similar compositionally to an organoarsenic compound rather than as inorganic As(V). 16S rRNA and arsenite oxidase gene (aioA) diversities were evaluated from biofilms and microbial mats from two geyser-discharge stream transects. Chloroflexi were the most prevalent bacterial group at flow distances where arsenite was converted to arsenate, corresponding to roughly 60o C. Some aioA-like gene sequences were homologous to alphaproteobacterial and undifferentiated beta- and gammaproteobacterial groups, but most of the genes were homologous to genomes from whole genomes of Chloroflexus aurantiacus. Potential importance of AioA protein amino acid sites was evaluated from aioA gene evolutionary trace analyses, and potential differences in the modes of electron transfer based on environmental geochemistry were identified. The research is expanding our understanding of possible microbial groups responsible for As cycling in geothermal habitats.   
El Tatio, Chile
Previous Support: National Science Foundation (EAR-0544960) 2006-2009
Dr. Philip Bennett and Dr. Chris Omleon, University of Texas-Austin
Dr. Megan Plenge, Trinity University

Dr. Vernon Phoenix, University of Glasgow, Scotland
Dr. Pablo Pastén of the Universidad Católica in Santiago, Chile

Related Publications from Group

Plenge, M.F., Engel, A.S., Omelon, C.R., Bennett, P.C. (2017) Thermophilic archaeal diversity and methanogenesis from El Tatio Geyser Field, Chile. Geomicrobiology Journal. 34: 220-230. doi:10.1080/01490451.2016.1168496. 

Engel, A.S., Johnson, L.R., Porter, M.L. (2013) Arsenite oxidase gene diversity among Chloroflexi and Proteobacteria from El Tatio Geyser Field, Chile. FEMS Microbiology Ecology. 83: 745–756. DOI: 10.1111/1574-6941.12030. 
Birdwell, J.E., Engel, A.S. (2010) Characterization of dissolved organic matter in cave and spring waters using UV-Vis absorbance and fluorescence spectroscopies. Organic Geochemistry. 41: 270-280.
Landrum, J.T., Bennett, P.C., Engel, A.S., Alsina, M., Pastén, P., Milliken, K. (2009) Partitioning geochemistry of arsenic and antimony, El Tatio Geyser Field, Chile. Applied Geochemistry. 24: 664-676. DOI:10.1016/j.apgeochem.2008.12.024   
Phoenix, V.R., Bennett, P.C., Engel, A. S., Tyler, S.W., and Ferris F.G. (2006) Chilean high-altitude hot spring sinters: a model system for UV screening mechanisms by early Precambrian cyanobacteria. Geobiology. 4: 15-28. 

Related Conference Abstracts from UTK Group

Myers, K.D., Engel, A.S., Omelon, C.R., Bennett, P.C. (2012) Physicochemical and biological zonation of high temperature silica and arsenic-rich streams at El Tatio Geyser Field, Chile. Abstract B43I-0542 presented at 2012 Fall meeting, AGU, San Francisco, CA, 3-7 December. (withdrawn poster presentation but abstract still available online)
Myers, K.D., Omelon, C.R., Engel, A.S., Bennett, P.C. (2011) The role of cyanobacteria in arsenic biogeochemistry at El Tatio Geyser Field, Chile. International Symposium for Environmental Biogeochemistry, Istanbul, Turkey, Sept. 25-30, 2011. (oral)
Engel, A.S., Johnson, L.R., Roy, A., Merchan, G. (2010) Microbial organoarsenical production in geothermal systems. Goldschmidt, Knoxville, TN. (oral presentation)
Johnson, L.R., Engel, A.S., Roy, A., Merchan, G. (2009) Geochemistry and microbial diversity of the arsenic cycle at El Tatio Geyser Field, Chile. Geological Society of American meeting, Portland, Oregon, October.
Franks, M., Omelon, C., Engel, A.S., Bennett, P.C. (2009) Correlations between archaeal diversity and geochemical parameters in an arsenic-rich hydrothermal system: 2009 EGU General Assembly, Geophysical Research Abstracts, 11: EGU2009-0. (oral)
Franks, M., Bennett, P., Omelon, C., Engel, A.S. (2008) Diversity of archaeal consortia in an arsenic-rich hydrothermal system. Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract B51D-0428. (poster presentation)
Engel, A.S., Birdwell, J.E., Johnson, L., Brannen, K.M., Franks, M., Omelon, C.R., Landrum, J.T., Alsina, M.A., Pasten, P.A., Bennett, P.C. (2008) Biofilm development, microbial diversity, and dissolved organic matter from El Tatio, Chile: implications for metalloid biogeochemical cycling. Geological Society of America Abstracts with Programs, 40: 295. (Invited oral presentation).
Franks, M.., Bennett, P.C., Omelon, C., Engel, A.S. (2007) Environmental controls on methanogen viability in the hydrothermal waters of the El Tatio geyser field, Chile. Eos Trans. American Geophysical Union, 88(52), Fall Meet. Suppl., Abstract B43A-0898. (poster presentation)
Landrum, J.T., Engel, A.S., Milliken, K., Bennett, P.C. (2006) Biogeochemistry of antimony and arsenic in hydrothermal fluids and opaline deposits from El Tatio geyser field, Chile. Geological Society of America Abstracts with Programs, 38: 546. (poster presentation)
Landrum, J., Engel, A. S., Milliken, K., Lansdown, J., Bennett, P. C. (2005) Distribution of antimony in silica geyserite from El Tatio, Chile, in Program and Abstracts of the Joint International Symposia for Subsurface Microbiology (ISSM 2005) and Environmental Biogeochemistry (ISEB XVII): Jackson Hole, WY. ASM, Washington, D.C., p. 64-65. (oral presentation)

Field Photographs

Geochemistry. Geomicrobiology. Geology. Ecology.

Interdisciplinary Research at the University of Tennessee