Spores of many common airborne fungi reveal no ice nucleation activity in oil immersion freezing experiments

[摘要] Fungal spores are ubiquitous biological aerosols, which are considered to actas ice nuclei. In this study the ice nucleation (IN) activity of sporesharvested from 29 fungal strains belonging to 21 different species was testedin the immersion freezing mode by microscopic observation of water-in-oilemulsions. Spores of 8 of these strains were also investigated in amicrodroplet freezing array instrument. The focus was laid on species ofeconomical, ecological or sanitary significance. Besides common molds(Ascomycota), some representatives of the widespread group of mushrooms(Basidiomycota) were also investigated.

Fusarium avenaceum was the only sample showing IN activity atrelatively high temperatures (about 264 K), while the other investigatedfungal spores showed no freezing above 248 K. Many of the samples indeedfroze at homogeneous ice nucleation temperatures (about 237 K). Incombination with other studies, this suggests that only a limited number ofspecies may act as atmospheric ice nuclei. This would be analogous to what isalready known for the bacterial ice nuclei.

Apart from that, we selected a set of fungal strains from different sites andexposed them to occasional freezing stress during their cultivation. This wasin order to test if the exposure to a cold environment encourages theexpression of ice nuclei during growth as a way of adaptation. Although thetotal protein expression was altered by this treatment, it had no significantimpact on the IN activity.

[学科分类] 地球化学与岩石