The Air Plasmidome: A Discreet Route for Pathogens and the Transmission of Antibiotic Resistance Genes?

Since the COVID-19 pandemic started, preventing airborne microorganism transmission has become everyone's concern. Viruses, bacteria, and fungal spores are airborne biological particles referring to bioaerosols. Through bacteria, a panel of genes (e.g., resistance or metabolic genes) might be found in bioaerosols and disseminated. Genes found on plasmids are potentially more exposed to the risk of transmissibility than those harboured by chromosomes. From 2422 air metagenomes analysed across various studies on bacteria, Proteobacteria were the most abundant microorganisms identified in air, with pathogens representing between 0.2% and 35.3% of the bacterial community per country. We identified 674,495 representative plasmids; 63,564 of them were linked to 5679 metagenome-assembled genomes. Among them, 89 plasmids were defined as keystones in terms of location numbers and plasmid coverage being more universal. Accessory traits of plasmids allow bacteria to adapt to their environment and contribute to host fitness. Antibiotic resistance genes represented < 1% of predicted plasmid genes and were mainly genes encoding efflux pumps. The plasmid similarity was significantly linked to the location and the microbial community (p < 0.001). Based on CRISPR detection, we determined that plasmids of bacteria coming from built environments and soils were overrepresented.