Geobiology: New Perspectives on Planet Earth

Friday, March 8th, 2002
Bruce Fouke
Event Description

A progressive integration of geology and microbiology, called Geobiology, is underway that will revolutionize our understanding of earth system processes and the history of life. This new research frontier focuses on the integration of recombinant DNA technology with chemical, sedimentologic, and hydrologic environmental analyses. This allows the complex interactions between organisms and their environments to be quantitatively tracked and will ultimately permit more accurate reconstruction of the biosphere from the ancient rock record. Bruce Fouke (UIUC Geology) and Abigail Salyers (UIUC Microbiology) have established a laboratory and assembled a research team that is dedicated to studies of modern and ancient molecular geobiology. Two initiatives are currently in progress, which include: (1) the role and source of bacteria responsible for coral disease in living reefs of the Netherlands Antilles and Papua New Guinea; (2) the control exerted by thermophilic bacteria on the shape and chemistry of carbonate mineralization at Mammoth Hot Springs, Yellowstone National Park.

Coral Disease Update: Distinct partitioning has been observed in the composition and diversity of bacterial communities inhabiting the surface and overlying seawater of three coral species infected with black bans disease (BBD) on the southern Caribbean island of Curacao, Netherlands Antilles. PCR amplification and sequencing of bacterial 16S rRNA genes with universally conserved rDNA primers has identified over 524 unique bacterial sequences affiliated with 12 bacterial divisions. The molecular sequences exhibited less than 5% similarity in bacterial community composition between seawater and the healthy, black band diseased, and dead coral surfaces. Clonelibraries from the BBD bacterial mat, which rapidly migrates across and kills the coral tissue, were comprised of eight bacterial divisions and 13% unknowns. Several sequences representing bacteria previously found in other marine and terrestrial organisms (including humans) were isolated from the infected coral surfaces, including Clostridium sp.,Arcobacter sp., Campylobacter sp., Cytophaga fermentans, C. columnaris, and Trichodesmium tenue. The presence of these and other affiliated sequences in the coral surface clone libraries may imply that human sewage, infection from other marine organisms, and terrestrial runoff may have combined to influence the development of BBD in corals on the Curacao reef tract.

Yellowstone Thermophiles Update: Five distinct environments of carbonate mineral deposits (called travertine) have been observed along spring outflow channels at Mammoth Hot Springs based on water chemistry and travertine crystal forms and chemistry. The aqueous chemistry of the host spring drainage system is dominated by CO2 degassing and dropping temperature. While these physical factors help drive the rapid precipitation of carbonate crystals to deposit travertine at rates as high as 5 mm/day, significant bacterial controls on travertine crystals form and isotope chemistry have been identified (e.g. crystals entombing and preserving the shape of filamentous Aquificales bacteria). Travertine isotope compositions indicate biological mediation during travertine deposition that increases in magnitude from the high (73oC) to the low (<25oC) temperature portions of the spring outflow. Preliminary bacterial 16S rRNA screening has revealed 187 bacteria sequences representing 21 bacterial divisions, which exhibit a remarkable 85% partitioning along the spring outflow. Changes in the chemical saturation of the spring water coincides with metabolic transitions from predominantly autotrophic to predominately heterotropic bacterial communities.

Bruce Fouke

Department of Geology