SURVIVAL OF A STROMATOLITE-BUILDING, EUKARYOTIC MICROORGANISM IN A CO2-RICH ATMOSPHERE

The eukaryotic, photosynthesizing protozoan Euglena mutabilis forms a biofilm layer on the surface of an acid mine drainage (AMD) channel at an abandoned coal mine site in western Indiana. E. mutabilis is a true acidophile that secrets mucilage to assist with attachment to the substrate. These biofilms are important because they contribute to the formation of Fe-rich stromatolites in the AMD channel by utilizing mucilage to trap and bind AMD chemical precipitates. Some Euglena species are reported to survive and reproduce in solutions purged with CO₂. This study examines the ability of E. mutabilis to survive in the presence of a pure CO₂ atmosphere. Cells reared in simulated AMD were placed in two containers with simulated AMD in an atmospheric glove box. An additional container was placed outside the glove box as a control. The ambient atmosphere in the glove box was replaced by CO₂. Additionally, CO₂ gas was used to purge one of the containers prior to running the experiment. During the experiment, oxygen was successfully purged from the glove box down to 0.2 mg/l. Cells were extracted from all containers at 12 h, 24 h, and 48 h and placed on a gridded thin section to count living versus dead cells. Cell counts showed 90% viable cells at each time interval indicating that E. mutabilis can survive in an almost pure CO₂ atmosphere for up to 48 hours. This study has important implications for understanding the viability of similar life forms under atmospheric conditions that may be reminiscent of low oxygen conditions on early Earth and other extraterrestrial environments. This study is also timely as we consider appropriate life forms for terraforming other celestial objects.