Microbial colonisation of polyethylene in offshore marine environments: Insights from the Southern and South Atlantic Oceans

Plastic debris is a pervasive environmental pollutant, with polyethylene (PE) among the most abundant floating polymers in marine environments. While microbial colonisation of marine plastics has been extensively documented, most studies focus on coastal waters in the Northern Hemisphere, leaving colonisation dynamics in remote Southern Hemisphere regions poorly understood. Here, we investigate early microbial colonisation of PE films incubated during two oceanographic transects across the Southern Ocean and South Atlantic Ocean. Using 16S rRNA gene amplicon sequencing and shotgun metagenomics, we assessed how geographic location, incubation regime (aquarium vs ship deck), and environmental factors (UV exposure, temperature, and salinity) shape microbial community structure and functional potential. Community composition was primarily influenced by transect location and incubation conditions, rather than material type. Dominant taxa included Cyanobacteria, Pseudomonadota, and Bacteroidota, taxa often associated with phototrophy, hydrocarbon degradation, and early surface colonisation. Functional analyses revealed enrichment in pathways related to biofilm formation, hydrocarbon degradation, lipid oxidation, and iron metabolism. These findings highlight how environmental conditions shape early plastisphere assembly and metabolic capabilities in understudied oceanic regions of the Southern Hemisphere.