Blue Observer
The large-scale abundance and distribution of antibiotic resistance genes (ARGs) within the atmosphere remain poorly documented, particularly over oceans. This study explores bacterial loads, diversity, and associated antimicrobial resistance genes in aerosols over the North Atlantic Ocean. Aerosol samples were collected from a ship during a cruise from Brest (France) to Woods Hole (USA) for 24-hour periods using a mast-mounted system, with additional one-hour spot samples taken daily and nightly using high-flow rates samplers. The airborne concentrations of bacteria along with 21 ARG subtypes as indicators of key resistance families were monitored using qPCR. These were related to the bacterial diversity obtained form same samples through ribosomal gene amplicon sequencing, and to the geographical origin of the air masses estimated using atmospheric dynamics models. Total ARG concentrations ranged from background concentrations of a few copies to > 105 copies/m3 of air. Near coasts, macrolide and tetracycline resistance genes were dominant (up to 93% and 38% of the total ARG monitored in the study, respectively). While sulfonamide resistance genes were also detected further offshore, those related to transposases and ß-lactamases were detected only sporadically. The multiple observed correlations between the aforementioned gene concentrations in the air and potential soil-derived microorganisms may be indicative of continental inputs. Conversely, the prevalence of quinolone resistance (qepA) in the air over the open ocean points toward a contribution from marine surfaces, supported by associations between several ARGs and marine microorganisms including cyanobacteria. These may thus act as environmental reservoirs of ARGs, and sources for further environmental spread notably by air means.