Windows into Darkness: LSU Research in the Subsurface

Life in the terrestrial subsurface was once considered to be a matter of fiction. The dogma was that life processes could not exist in complete darkness, without the input of photosynthetically generated food and energy. Therefore, if there was life, it would have meager abundances and eke out an existence without any impact to its surroundings. Recently, however, abundant and flourishing microbial life has been found inhabiting nearly every subsurface environment that scientists have cared to look. The microorganisms scavenge nutrients from rocks and harness vast amounts of chemical energy, sometimes serving as the base of complex, subsurface ecosystem.

Although Dr. Annette Summers Engel and her students in the Geomicrobiology and Environmental Microbiology Studies (GEMS) group at Louisiana State University study subsurface geomicrobiology by various means, including through aquifer wells, they prefer to study caves. Engel, who got her start in geology at the tender age of 12 while exploring caves in Kentucky, states that, “If cave research was easy, someone would have already done it. Caves are one of the last remaining places on Earth that are virtually untouched by humans, and few people have seen some of the places that we get to visit.”

Using caves as natural windows into the subsurface, the GEMS group has several broad research goals that apply to all of their research projects, including determining the diversity of organisms living in the subsurface, evaluating how the microbes have come to colonize so many different subsurface environments, understanding how microorganisms have interacted with geological materials through time, and quantifying how and to what extent microbial activities influence biogeochemical cycles. The GEMS group, along with their collaborators around the world, are compiling a database of microbes that they have identified from caves all over the world using culture and non-culture based techniques.

After nearly ten years of conducting research in caves, Engel has discovered several previously unknown groups of bacteria that appear to be adapted to living in a certain type of cave habitat, one that is rich in reduced sulfur compounds. Engel and her students are evaluating how geographic and hydrogeologic separation may control the genetic evolution of these special microbes in the subsurface. According to Engel, “Studying these microbes from caves is allowing us to differentiate among the mechanisms that govern the distribution of microbes on Earth. Unless the caves are geographically close to each other, caves are not usually connected, and microbes living in one cave may not be in genetically related to, or even in genetic communication with, the microbes from another cave.” So far, the research group has found that some microbial evolutionary lineages are only found in one cave, but other lineages are ubiquitously distributed in caves with similar geochemical and geological conditions.

For more information on the LSU GEMS group refer to:  http://geol.lsu.edu/aengel/research_areas.htm