Refining Our Approach to Extraterrestrial Life Detection: An Investigation of Microbial Communities in Mineral Environments

The discovery of lava caves on Mars and lunar terrains has promoted the study of analogous environments on Earth to enhance our ability to detect life on extraterrestrial bodies. One such environment is the mineral deposits in caves that appear non-biological, but reveal diverse microbial communities upon examination. The goal of this study is to identify biosignatures associated with microbial communities within mineral deposits from high altitude caves from Hawai’i (U.S.A.). Biosignatures are investigated with scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), which provides elemental analysis of the sample to identify carbon-dominated regions, indicating living matter. SEM/EDX also allow us to study the interactions between the microorganisms and the mineral environment in which they reside. Samples taken from Arisa, Blair and Cloud caves in Hawai’i were examined. The sample from Arisa cave was taken from a yellow-gold deposit on the cave wall surface. EDS shows that the deposit is an iron oxide with some gypsum present. Structures in the sample that appeared to be biological generally produced a signal indicating high carbon content. The putative microorganisms, fuzzy filaments and coccoid morphologies, are present in biofilms. Results of this study include a comparison of microorganisms from different caves, and an investigation of whether the iron oxides present are biogenic. Future studies include culture-independent studies of the microbial communities residing in these mineral-biological deposits. These studies will help in life detection efforts on extraterrestrial bodies and expand our knowledge of the microbial communities of oligotrophic caves.