G eomicrobiology
&

E nvironmental

M icrobiology

S tudies   

Our ability to reconstruct the past sulfur cycle is hampered by our limited understanding of the nature and behavior of sulfur gases, primarily because it is difficult to measure gas movement into, out of, or through sedimentary systems. With Dr. Alexander Prange and Dr. Josef Hormes, we are identifying and resolving the speciation of inorganic and organic sulfur species, including gases, which link geological and geochemical processes to biological processes. This work is currently funded by NSF.

We recently produced the first sulfur K-edge X-ray Absorption Near-Edge Structure (XANES) spectra for gases that were evacuated and evolved from simple sulfur-bearing solids that were incrementally heated to ~400 ^oC. XANES is one of the most efficient tools to study sulfur speciation in biogeochemical systems. Previously, there were few examples of sulfur gas XANES spectra; compounds were gases at room temperature or liquids under high vapor pressure. This work is being done at the LSU Center for Advanced Microstructures and Devices (CAMD).

The application of this new gas-phase XANES technique expands our ability to evaluate sulfur speciation in all phases in order to address three main research questions:

• What sulfur speciation changes occur when sulfur-bearing inorganic and organic solids are heated?

• Does the composition of the precursor sulfur-phase (e.g., mineralogy, organic matter sulfur content) influence the type of condensed sulfur phase(s) in a system?

• Can the signature of microbial processes (e.g., isotopic) be differentiated from low-temperature geological (e.g., diagenetic) processes?

Changes in sulfur species and the classification of reaction byproducts from different experiments, during heating to temperatures <200^o C, will be examined by using XANES. Simultaneous collection of gas-phase XANES spectra and masses (i.e. isotopic compositions) using quadrupole mass spectrometry will identify novel gases. The research promises to reveal a unique depiction of the types of sulfur species associated with diagenetic reactions and of the connection between volatile and condensed sulfur species in biogeochemical systems. The work will increase our understanding of how possible geochemical and metabolic processes related to the sulfur cycle have been recorded, and even altered, throughout Earth’s history.

We are currently seeking applications for new PhD graduate students to participate with the project.

References for this research

Linking nutrient cycling to biodiversity in microbial ecosystems

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.

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. 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.

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.

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 :  


(link to research description on NSF website)

Image from CAMD Experimental Hall.

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

Stay tuned for more data and research results!