The rising occurrence of microbial antibiotic resistance genes (ARGs) in the natural environments poses a significant threat to ecosystem health and human welfare. Anthropogenic activities, particularly related to farming and wastewater treatment plants have boosted the spread of ARGs in the coastal waters, yet their prevalence and distribution within marine microorganisms remain underexplored. This study investigates the occurrence of ARGs in marine bacteria from anthropogenically influenced surface waters of the North and Baltic seas and the pristine waters of West Greenland.
Samples were collected with a sea-surface microlayer sampling catamaran and with conventional Niskin bottles attached to a CTD rosette. The extracted DNA was sequenced using Illumina NGS to obtain a set of metagenomically assembled genomes that were clustered into 580 genomic operational taxonomic units (gOTUs). The identified ARGs were analyzed using both established alignment search tools as well as novel deep learning-based algorithms.
Results revealed that over 85% of the analyzed gOTUs contain at least one multidrug resistance gene. Resistances to vancomycin, phenicol, and beta-lactam were widespread, even in the samples from West Greenland. Some specific ARGs like tolC, associated with multidrug efflux pumps, and bcr which encodes bicyclomycin resistance, were found across all sampling sites. Most of the ARGs were located on chromosomes rather than plasmids, and only a small number of identified gOTUs contained virulence factors. This suggests that ARGs in marine bacteria generally do not pose a direct threat to human health, however, they may serve as an expanding reservoir of ARGs with unknown repercussions on the human society.
 

marine bacteria,surface microlayer,antibiotic resistance,resistome