Abstract
Abstract. Archaea are widespread and abundant in many terrestrial and aquatic environments, and are thus outside extreme environments, accounting for up to ~10% of the prokaryotes. Compared to bacteria and other microorganisms, however, very little is known about the abundance, diversity, and dispersal of archaea in the atmosphere. By means of DNA analysis and Sanger sequencing targeting the 16S rRNA (435 sequences) and amoA genes in samples of air particulate matter collected over 1 year at a continental sampling site in Germany, we obtained first insights into the seasonal dynamics of airborne archaea. The detected archaea were identified as Thaumarchaeota or Euryarchaeota, with soil Thaumarchaeota (group I.1b) being present in all samples. The normalized species richness of Thaumarchaeota correlated positively with relative humidity and negatively with temperature. This together with an increase in bare agricultural soil surfaces may explain the diversity peaks observed in fall and winter. The detected Euryarchaeota were mainly predicted methanogens with a low relative frequency of occurrence. A slight increase in their frequency during spring may be linked to fertilization processes in the surrounding agricultural fields. Comparison with samples from the Cape Verde islands (72 sequences) and from other coastal and continental sites indicates that the proportions of Euryarchaeota are enhanced in coastal air, which is consistent with their suggested abundance in marine surface waters. We conclude that air transport may play an important role in the dispersal of archaea, including assumed ammonia-oxidizing Thaumarchaeota and methanogens.
Highlights
Archaea have long been thought to occur only in restricted, extreme environments
From the 47 air filters sampled at Mainz, Germany (Table S1), we retrieved a total of 435 archaeal 16S rRNA gene sequences that grouped into 57 operational taxonomic units (OTUs)
We found the abundance of archaea in air to be only between ∼ 1 and ∼ 10 gene copies per cubic meter of air, while that of bacteria was found to be ∼ 104 to ∼ 106 in the same air samples (Table S4)
Summary
Archaea have long been thought to occur only in restricted, extreme environments. Since their formal recognition as an independent domain of life about two decades ago (Woese et al, 1990), they have been found in a wide variety of habitats from hydrothermal vents to aquatic and soil environments (Auguet et al, 2010; Bintrim et al, 1997; Boetius et al, 2000; Jurgens et al, 2000; Ochsenreiter et al, 2003; Schleper et al, 1997; Takai et al, 2001). While the atmosphere may not be a key habitat of archaea, it may act as the primary medium for the dispersal of microorganisms among the different ecosystems on the Earth’s surface (Fröhlich-Nowoisky et al, 2012).
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