Evaluating the potential for Archaea to serve as ice nucleating particles

Abstract. Aerosols play a crucial role in cloud formation. Biologically-derived materials from microorganisms such as plant bacteria, fungi, pollen, and various vegetative detritus can serve as ice nucleating particles (INPs), some of which initiate glaciation in clouds at relatively warm freezing temperatures. However, determining the magnitude of the interactions between clouds and biologically-derived INPs remains a significant challenge due to the diversity and complexity of bioaerosols, and limited observations of such aerosols to facilitate cloud ice formation. Additionally, microorganisms from the domain Archaea have to date not been evaluated as INPs. Here, we present the first results reporting the ice nucleation activity of a subset of archaeal cells from Haloarchaea. Intact cells of Halococcus morrhuae and Haloferax sulfurifontis demonstrated the ability to induce freezing as warm as −18 ˚C, while lysed cells of Haloquadratum walsbyi and Natronomonas pharaonis were unable to serve as warm temperature INPs. Exposure to heat and peroxide digestion indicated that the INPs of intact cells were driven by organic (H. morrhuae and H. sulfurifontis) and possibly also heat-labile materials (H. sulfurifontis only). While halophiles are prominent in hypersaline environments such as the Great Salt Lake and the Dead Sea, other members of the Archaea, such as methanogens and thermophiles, are prevalent in anoxic systems in seawater, sea ice, marine sediments, glacial ice, permafrost, and other cold niches. Archaeal extremophiles are both diverse and highly abundant. Thus, assessing their ability to become airborne, and their abilities to impact cloud formation, is necessary to improve understanding of biological impacts on clouds.