Amato, P. | Search bioRxiv

bioRxiv2023

Clouds, oases for airborne microbes. Differential metagenomics/ metatranscriptomics analyses of cloudy and clear atmospheric situations

Bacteria cells and fungal spores can aerosolize and remain suspended in the atmosphere for several days, exposed to water limitation, oxidation, and lack of nutrients. Using comparative metagenomics/metatranscriptomics, we show that clouds are associated with the activation of numerous metabolic functions in airborne microorganisms, including fungal spore germination. The whole phenomenon mirrors the rapid recovery of microbial activity in soils after rewetting by rain, known as the "Birch effect". Insufficient nutrient resources in cloud droplets cause a famine that recycling cellular structures could alleviate. The recovery of metabolic activity by microorganisms in clouds could favor surface invasion upon deposition, but it may also compromise further survival upon cloud evaporation. In any case, clouds appear as floating biologically active aquatic systems. One-Sentence SummaryClouds activate metabolic processes in airborne microorganisms

ecology↗

bioRxiv2023

Experimental and methodological framework for the assessment of nucleic acids in airborne microorganisms

Studying airborne microorganisms is highly challenging due to ultra-low and spread biomass, and great spatial and temporal variabilities at short scales. Aeromicrobiology is still an emerging discipline of environmental microbiology, and some of the basic practices (replication, control of contaminants, etc) are not yet widely adopted, which potentially limits conclusions. Here we aim at evaluating the benefits of such practices in the study of the aeromicrobiome using molecular-based approaches, and recommend the following: (i) sample at high airflow rate, if possible into a fixative agent, in order to be able to capture specific situations ; (ii) replicate sampling and process samples individually to enable statistical analyses ; (iii) check for contaminants at different steps of the analytical process, and account for their potential stochasticity in sequence decontamination methods ; (iv) include internal references to verify qualitative and quantitative aspects of the data, and (v) eventually investigate multiple analytical procedures to identify potential impacts on the data. In our study, samples were collected at a remote mountain site using high-flow rate impingers collecting airborne material into nucleic acid preservation buffer. As high of [~]75% of the sequences were shared between independent triplicates, gathering 28 to 38% of the richness observed at the ASV level at a given sampling date, which also emphasizes spatial heterogeneity at short scale due to rare taxa. Thanks to replicates, daily variations in the diversity of bacteria could be distinguished statistically, and the inevitable presence of contaminating sequences in controls could be accounted for using established statistical methods. This work opens new perspectives and notably paves the way to untargeted molecular methods in the exploration of aeromicrobiomes composition and functioning. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=152 SRC="FIGDIR/small/561683v1_ufig1.gif" ALT="Figure 1"> View larger version (54K): org.highwire.dtl.DTLVardef@48bddcorg.highwire.dtl.DTLVardef@1a8c3fforg.highwire.dtl.DTLVardef@dba98forg.highwire.dtl.DTLVardef@159055e_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗