Jellyfish blooms - an overlooked hotspot and potential vector for the transmission of antimicrobial resistance in marine environments

Jellyfish, and gelatinous zooplankton (GZ) in general, represent an important component of marine food webs. Certain GZ species are capable of generating massive blooms of severe environmental impact. These blooms are often followed by a sudden collapse of the entire population, introducing considerable amounts of organic matter (GZ-OM) in the oceans interior. GZ-OM represents an abundant substrate to promote bacterial growth and copious colonizable surface for microbial interactions. Hence we hypothesized that this GZ-OM serves as a yet overlooked hotspot for transmitting antimicrobial resistance genes (ARGs) in marine environments. For this we experimentally evolved and analyzed marine microbial communities in microcosms in presence and absence of OM from scyphozoan Aurelia aurita s.l. and ctenophore Mnemiopsis leidyi. Communities evolved under GZ-OM exposure displayed an up to 4-fold increase in relative ARG and an up to 10-fold increase in abundance of horizontally transferable mobile genetic elements (MGEs) per 16S rRNA gene copy compared to the controls. This trait was consistent across ARG and MGE classes and independent of the GZ species, suggesting that the underlying mechanism is indeed based on the general influx of nutrients and colonizable surfaces. Potential ARG carriers included known key GZ-OM degraders, but also genera containing potential pathogens hinting towards an increased risk of ARG transfer to pathogenic strains. Here, Vibrio were pinpointed as potential key species directly associated with several significantly elevated ARGs and MGEs. Subsequent whole-genome sequencing of a Vibrio isolate from the microcosm experiment revealed the genetic potential for the mobilization and transfer of ARGs in GZ-OM degrading microbial consortia. With this study, we established the first link between two emerging issues of marine coastal zones, jellyfish blooms and AMR spread, both likely increasing in projected future ocean scenarios.