Testing the Efficiency of Various Halophilic Archaea as Ice Nucleating Particles

Solutions with 5% salt are classified as brines and are usually uninhabitable by most organisms. On the other hand, halophilic archaeal microorganisms require these conditions to proliferate and have been found in hypersaline terrestrial lakes, subsurface aquifer seeps, deep-sea brine pools, and sea-ice brine channels. Marine micro-biomass around the world has been known to produce a microscopic biofilm at the surface of the ocean composed of biogenic and biological particles which then become airborne and work as both cloud condensation nuclei and ice nucleating particles (INPs). This study investigates 4 well-known easy to grow haloarchaeal species, Haloferax sulfurifontis, Natronomonas pharaonsis, Haloquadratum walsbyi, and Halococcus morrhuae, and how they perform as INPs due to their expansive dominance in some of the world’s largest hypersaline environments like the Great Salt Lake and interconnected brine channels in sea-ice. Stock solutions of each species were tested under 4 different conditions, ultra-pure water with 10% and 1% stock concentrations and 20% hypersaline solution with 10% and 1% stock concentrations. The hypersaline solution was used to recreate more natural environments and to avoid cells from lysing. Methodology of this investigation utilizes drop freezing assays on a cold plate apparatus to simulate cloud ice nucleation. Results have clearly demonstrated each species has a unique effect on the freezing temperatures with H. walsbyi under ultra-pure 10% condition being the most effective INP initiating freezing at an average (-16.5. Both H. walsbyi and H. sulfurifontis consistently performed well under all 4 conditions shifting the freezing curve towards warmer temperatures. These are the first reported results of ice nucleating capabilities of any haloarchaea which will hopefully encourage future studies into understanding natural sources of INPs.