Biogeo. cycle A.W

“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-1and ~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.”

Summary:  We have long known about the microbial presence within clouds but until recently most of our data has been a result of cell culturing which as we all know: may not be representative of the microbial community. This study via the use of 16s amplicon sequencing sought to define both the taxonomic identity and microbial activity via extracted DNA and RNA respectively. Atmospheric samples were taken periodically above France via a modified weather probes. Each sample was screened for the relative amount of industrial contaminants to serve as a comparison to the negative control. This study found that on average 11000 to 21000 distinct OTUs which is comparable to that of a typical soil sample. Prokaryotes made up the majority of the sample with low amounts of eukaryotic fungal populations also being present.  The source of this diversity has been attributed to aerosols particulate products that resulted from saphorytes. The Microbial richness of the aforementioned microbes was more pronounced in the contaminated samples. Between all the samples it was evident that the metabolic functions of these microbes were important for many hydrological mechanisms such as ice nucleation and ion mediated chemistry reactions which aid in both the formation of water droplets and the act of precipitation respectively. The microbiome of the cloud was found to be variable depending on the location and sensitive to changes in resources (such as industrial contaminants, temperature and topography) so further study should be allocated to defining, and in the far future, altering the clouds’ microbiome.    

Amato P, Joly M, Besaury L, Oudart A, Taib N, Moné AI, et al. (2017) Active microorganisms thrive among extremely diverse communities in cloud water. PLoS ONE 12(8): e0182869.

Leave a Reply