Life aloft: exploration of the diversity and activity of atmospheric microbes
Creators: name: Dillon, Kevin Patrick
Publisher: name: No Publisher Supplied
Year: 2021

description: There are diverse and active microorganisms, or microbes, in the atmosphere, which are found across atmospheric compartments such as clouds, precipitation, and air. Airborne microbial guilds associated with the metabolism of two greenhouse gases, carbon dioxide and methane, as well as a potential product, methanol, have been detected in the atmosphere. These compounds were investigated as substrates for metabolism by airborne microbes. Specifically, the microbial guilds of interest were microbial oxygenic photoautotrophs (cyanobacteria and algae), methanotrophs, and methylotrophs. One of the main greenhouse gases in the atmosphere is carbon dioxide, which can be incorporated by cyanobacteria and algae. Their diversity in clouds and rain were investigated around puy de Dôme, France. Cyanobacteria, diatoms, as well as red, golden, and green algae were detected through a combination of cultivation, metagenomics, and amplicon-based analyses of cloud water. Of these groups, green algae of the Chlorellaceae were cultured from cloud water. Additionally, rain water was collected and the abundance of chlorophyll-a containing cells and the diversity of green algae and cyanobacteria were assessed with targeted amplicon sequencing. Green algae of the Trebouxiales and cyanobacteria of the Chroococcidiopsidales were found to be recurrent members of the microbial population in rain. These microbes survived despite the stressors associated with suspension in the atmosphere and likely use it as a dispersal vector. Furthermore, these microbes have the potential to metabolize carbon dioxide while transiting through the atmosphere.Another greenhouse gas of interest that is metabolized by microbes is methane. In previous studies, methanotrophic bacteria have been detected in air and other bacteria have been found to be active in the air outside of water droplets. Because the average residence time of airborne bacteria is long enough for growth to occur and there would be in situ exposure to methane, methanotrophs might be able to grow in the air outside of water droplets. In this study, methanotrophic bioaerosols were characterized in gas-phase bioreactors and their ability to grow on methane was assessed by DNA-stable isotope probing (SIP). Out of seven experiments, three experiments suggest that aerial methanotrophs grew on methane. Humidity was likely a major factor as to whether the bacteria could grow on methane in the airborne state.Through abiotic and biotic processes, methane can be converted to methanol, which is metabolized by methylotrophic bacteria. An aerotolerant methylotroph, Methylorubrum extorquens D2, was isolated from a methanotrophic air enrichment. The bacterium was able to survive in the air for extended periods of time. Furthermore, its genome encoded for various proteins associated with desiccation, DNA repair, general stress response, and carbon metabolism. All these predicted proteins would be important for Methylorubrum extorquens D2’s survival and potential metabolism of a carbon compound such as methanol in the atmosphere. Overall, this research contributes to the growing body of knowledge about the diversity and activity of the atmospheric microbiome.