G eomicrobiology
&

E nvironmental

M icrobiology

S tudies   

Nutrient cycling - carbon, sulfur, and nitrogen

We could easily study microbial processing and nutrient cycling in surface settings (e.g., lakes, ponds, shallow marine sediments, soils, etc.), but these habitats are overrun by phototrophic organisms. Because the subsurface is thought to have more biomass, predominately as microorganisms, than surface environments, there is a fundamental need to understand life processes that occur in complete darkness. Moreover, identifying how microorganisms obtain energy and how nutrients are conserved and cycled in modern ecosystems will elucidate how life and metabolic processes evolved on Early Earth and what types of biosignatures accurately record the processes of that Early life.

We study microbes from aphotic (cave) habitats because it allows us to understand life processes that are not dependent on sunlight. If organisms are to survive in the subsurface, they either have to rely on either allochthonous or autochthonous sources (respectively, derived from the someplace else or produced in situ). Allochthonous nutrient sources can include water infiltrating from surface runoff, whereas autochthonous sources are made by microbes themselves. Chemolithoautotrophic microorganisms produce their own carbon energy and nutrition from inorganic chemical energy.

At LSU, we are using state-of-the-art techniques, including synchrotron-based x-ray adsorption near-edge spectroscopy (XANES) at the Center for Advanced Microstructures and Devices (CAMD) and fluorescence spectroscopy to understand the variety of sulfur and carbon compounds present, and produced, in microbial subsurface ecosystem. We also apply stable isotope methods to characterize carbon, sulfur, and nitrogen cycling in microbial systems, including in caves and karst aquifers. Other nutrient cycling (and preservation of metals in the rock record) interests include the chromium, arsenic, and antimony systems.

References for this research

Diversity of Sulfur-based Microbial Ecosystems

Dr. Engel and the GEMS group study with a variety of microbial groups that live in subsurface habitats, but one microbial group that we are especially interested in are sulfur bacteria.

Epsilonproteobacteria. Novel epsilonproteobacterial groups, closely related to microbes found in groundwater (sometimes associated with hydrocarbon contamination) and at deep-sea hydrothermal vents, have been found in caves with hydrogen sulfide-rich spring water and at surface-discharging sulfidic springs. Very little is known about these bacteria from terrestrial settings, mostly because there have been few investigations.

To understand the biogeography and evolutionary history of the terrestrial groups, cave and spring systems are being sampled. Our working hypothesis is that these bacteria are important for local (to global) biogeochemical cycling in the carbonate geologic settings. 

The Lower Kane Cave & Edwards Aquifer Project Website

The Frasassi Caves Project

Epsilonproteobacteria in Terrestrial Springs and Caves Project Website

References for this research
 

This research is being supported by :

White filaments of Epsilonproteobacteria in Lower Kane Cave, Wyoming. Photo by A.S. Engel.

Sulfur-oxidizing bacteria. Bright spots are intracellular sulfur globules.
Photo by A.S. Engel.

Stay tuned for more data and research results!