Bioaerosols and atmospheric ice nuclei in a Mediterranean dryland: community changes related to rainfall

Abstract

Abstract. Certain biological particles are highly efficient ice nuclei (IN), but the actual contribution of bioparticles to the pool of atmospheric IN and their relation to precipitation are not well characterized. We investigated the composition of bioaerosols, ice nucleation activity, and the effect of rainfall by metagenomic sequencing and freezing experiments of aerosol samples collected during the INUIT 2016 campaign in a rural dryland on the eastern Mediterranean island of Cyprus. Taxonomic analysis showed community changes related to rainfall. For the rain-affected samples, we found higher read proportions of fungi, particularly of Agaricomycetes, which are a class of fungi that actively discharge their spores into the atmosphere in response to humidity changes. In contrast, the read proportions of bacteria were reduced, indicating an effective removal of bacteria by precipitation. Freezing experiments showed that the IN population in the investigated samples was influenced by both rainfall and dust events. For example, filtration and heat treatment of the samples collected during and immediately after rainfall yielded enhanced fractions of heat-sensitive IN in the size ranges larger than 5 µm and smaller than 0.1 µm, which were likely of biological origin (entire bioparticles and soluble macromolecular bio-IN). In contrast, samples collected in periods with dust events were dominated by heat-resistant IN active at lower temperatures, most likely mineral dust. The DNA analysis revealed low numbers of reads related to microorganisms that are known to be IN-active. This may reflect unknown sources of atmospheric bio-IN as well as the presence of cell-free IN macromolecules that do not contain DNA, in particular for sizes < 0.1 µm. The observed effects of rainfall on the composition of atmospheric bioaerosols and IN may influence the hydrological cycle (bioprecipitation cycle) as well as the health effects of air particulate matter (pathogens, allergens).

Respirable Metals, Bacteria, and Fungi during a Saharan–Sahelian Dust Event in Houston, Texas

“…Most fungal OTUs were designated to Ascomycota (58.5%) and Basidiomycota (38.8%), the kingdom’s two largest phyla ( Figure heatmap). ,, Dominant fungal classes (Figure top panel) were Agarimicomycetes (36.7%), Dothideomycetes (31.5%), Sordariomycetes (15.1%), and Eurotiomycetes (10.1%). Agaricomycetes are a large class of wood-decaying spore-forming fungi that have been detected in aerosolized form . Dothideomycetes contain several plant pathogens as well as saprobic fungi found in soils and freshwater habitats …”

“…Our work also suggests that it might be important to investigate the oxidative potential of bioaerosols in conjunction with metals. Together, they could generate reactive oxygen species, which are thought to be a good indicator of toxicity. ,, This work could also be useful in identifying mineral dust and bioaerosols that are nuclei for cloud condensation and ice formation, thereby influencing the radiation budget, climate, and the hydrological cycle. ,, …”

“…Agaricomycetes are a large class of wood-decaying spore-forming fungi that have been detected in aerosolized form. 56 Dothideomycetes contain several plant pathogens as well as saprobic fungi found in soils and freshwater habitats. 79 At the genus level, dust intrusion caused a strong dilution of Peniphora (Peniophoraceae), which constituted roughly a third of all measured genera on S1.…”

About the Biodiversity of the Air Microbiome

“…The diversity of the indoor mycobiome may depend on outdoor air pollution, as was shown in a study conducted in Beijing [ 74 ]. Similar to the bacterial microbiome, the mycobiome composition may vary depending on particular meteorological events: for example, the content of fungi belonging to the class Agaricomycetes/Basidiomycota [ 86 ], which release vast quantities of spores into the atmosphere after rains, increased significantly after a rain over the arid area of the Mediterranean.…”

“…Разнообразие микобиома внутри помещений может зависеть от загрязнения воздуха снаружи, как показано при исследовании в Пекине [74]. Как и в случае бактериобиома, состав микобиома может меняться в зависимости от конкретных метеорологических событий: так, после дождя над засушливой территорией Средиземноморья существенно повышалось содержание грибов класса Agaricomycetes/ Basidiomycota [86], которые после дождей выпускают огромное количество спор в воздух.…”