Abstract
Clouds are key components in Earth’s functioning. In addition of acting as obstacles to light radiations and chemical reactors, they are possible atmospheric oases for airborne microorganisms, providing water, nutrients and paths to the ground. Microbial activity was previously detected in clouds, but the microbial community that is active in situ remains unknown. Here, microbial communities in cloud water collected at puy de Dôme Mountain’s meteorological station (1465 m altitude, France) were fixed upon sampling and examined by high-throughput sequencing from DNA and RNA extracts, so as to identify active species among community members. Communities consisted of ~103−104 bacteria and archaea mL-1 and ~102−103 eukaryote cells mL-1. They appeared extremely rich, with more than 28 000 distinct species detected in bacteria and 2 600 in eukaryotes. Proteobacteria and Bacteroidetes largely dominated in bacteria, while eukaryotes were essentially distributed among Fungi, Stramenopiles and Alveolata. Within these complex communities, the active members of cloud microbiota were identified as Alpha- (Sphingomonadales, Rhodospirillales and Rhizobiales), Beta- (Burkholderiales) and Gamma-Proteobacteria (Pseudomonadales). These groups of bacteria usually classified as epiphytic are probably the best candidates for interfering with abiotic chemical processes in clouds, and the most prone to successful aerial dispersion.
Highlights
The atmospheric envelope is a fundamental component of Earth’s functioning
The air is dotted with microorganisms originating from surface habitats like vegetation, soil, water, or Humans/animals among natural sources [6,7,8], at concentrations varying from ~102 to ~106 cells m-3
The basic biological, chemical and meteorological features of the cloud water samples investigated are shown in Table 1; these were usual for clouds collected at the Puy de Dome Mountain’s atmospheric observatory [40,58]
Summary
The atmospheric envelope is a fundamental component of Earth’s functioning. Apart from holding huge energy exchanges, it transports, transforms and redistributes material at a large scale; it participates to the spreading of microorganisms over the globe (e.g., [1,2,3,4,5]). The air is dotted with microorganisms (virus, bacteria, archaea, and eukaryotes) originating from surface habitats like vegetation, soil, water, or Humans/animals among natural sources [6,7,8], at concentrations varying from ~102 to ~106 cells m-3 Some of them are regarded with attention for potential health hazards to Humans, animals and plants [11].
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