Evaluating the potential for Haloarchaea to serve as ice nucleating particles

Aerosols play a crucial role in cloud formation. Biologically derived materials from bacteria, fungi, pollen, lichen, viruses, algae, and diatoms 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 facilitating 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 four species in the class Haloarchaea. Intact cells of Halococcus morrhuae and Haloferax sulfurifontis demonstrated the ability to induce immersion freezing at temperatures up to -18 degrees C, while lysed cells of Haloquadratum walsbyi and Natronomonas pharaonis were unable to serve as immersion 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, it is important to assess their ability to serve as INPs as it may lead to an improved understanding of biological impacts on clouds.

Automated summary

Aerosols play a crucial role in cloud formation, with biologically derived materials serving as ice nucleating particles, but the diversity and limited observations of bioaerosols make it challenging to determine the magnitude of their interactions with clouds. Extremophiles from the domain Archaea, including halophiles like the ones found in hypersaline environments, demonstrate the ability to induce ice formation, suggesting the importance of evaluating their impact on clouds.