Amazonian rainforest bioaerosol influenced by African dust intrusion

Biological particles are a substantial component of Amazonian aerosols, yet their community composition, spatiotemporal variability, and atmospheric impacts remain poorly understood. Here, we present a comprehensive study of archaeal, bacterial, and fungal bioaerosol communities in the Amazon rainforest, collected at 42 m and 323 m height above ground at the Amazon Tall Tower Observatory (ATTO). Archaea exhibited overall low prevalence, dominated by potential marine clades. Under rainforest background conditions, the bacterial community varied strongly with time and height, indicating an inhomogeneous source distribution and strong long-range influence. In contrast, the fungal bioaerosol community exhibited low variability over time and height, suggesting persistent, widespread, and uniform regional sources. During an African dust intrusion, the bacterial community composition changed drastically. A strong increase in relative sequence abundance of bacteria belonging to the phylum Bacillota, known to be abundant in Saharan dust, suggests a substantial influx of bacterial bioparticles and genetic material from Africa. In contrast, the fungal community remained unaffected, likely due to a masking effect of local emissions. During the dust event, the total mass concentrations of coarse mode aerosol particles (>1 µm) and of atmospheric endotoxins, that can trigger respiratory diseases, increased by factors up to 4. This study serves as a key foundation to unravel the mechanisms of bioparticle and dust cycling and their effects on biodiversity, climate, and public health during Earth history up to current and future environmental conditions in the Anthropocene.