Microbial growth and distribution in layered ices relevant to Mars

Abstract

Layered ice systems are analogs of natural environments expected on Mars. The presence of liquid water on Mars suggests that life may exist inside brine trapped between layers of pure water ice accumulated from frost and aeolian dust deposits. We are investigating the proliferation and survival of bacterial cells entrapped in layered ice systems under laboratory conditions by freezing and melting brine layers at low temperatures. Halophilic bacteria (Halomonas sp. str. GSP3, Halomonas sp. str. BLE7, and Oceanobacillus sp. str. SAF16) were isolated from JPL SAFs, Basque Lake, and the Great Salt Plains. Cultures were grown at a high salt concentration (15% NaCl) in R2A medium and frozen brine layers were formed at -40°C. The brine layer was melted at -12°C and allowed to fractionate into dense liquid brine and a frazil ice layer, while top and bottom layers of pure water remained frozen. The microbes were in the brine layer to monitor their survival, activity and movement throughout the brine, frazil, and pure water ice layers. Microbial cells may exhibit migration patterns within the layered ice systems, as we observe cell partitioning and distribution. All three bacterial species exhibited high survival rates and appeared to partition more cells in the brine layer than the frazil layer. We are extending our research by creating layered ice analogs with NaClO3 salts, which have extremely low freezing points and are common on Mars. This project will help us monitor the activity of microbes in Mars-like conditions through layered ice systems and inform planetary protection protocols. The layered ice systems assist in studying the characteristics of these halophilic microbes and their potential to survive in entrapped layered ices. Supported by NASA and K-INBRE.