Comparative functional profiles of microbial communities on drifting microplastics and volcanic pumice.

Plastics have been shown in incubation experiments to select for distinct microbial communities from biogenic and inanimate controls, with successional shifts over time. However, few field studies have directly compared microbial communities on free-drifting plastic debris and non-plastic particles. Using shotgun metagenomics, we analyzed the microbial communities adhered to marine microplastics and co-drifting volcanic pumice as a time-tracked control to investigate differences in metabolic potential. Overall, the mature microbial communities on neuston-net collected microplastics and pumice exhibited broad functional and taxonomic similarity, providing suggestive evidence of function convergence. Interestingly, plastic hydrolysis genes, and putative hydrocarbon-degrading bacteria were scarce on both substrates, whereas β-glucan degradation genes were abundant, indicating potential utilization of biofilm-associated carbon sources. Nevertheless, pumice biofilms exhibited substrate-associated enrichment of genes linking to biofilm formation, quorum sensing, nitrogen and phosphonate metabolism, suggesting expanded genomic versatility. Considering the increasing input of anthropogenic and natural inanimate particles may act as environmental perturbations, potentially shaping microbial succession and metabolic potential on floating surfaces. Our findings provide insight into the genomic potential of particle-associated assemblages that stay afloat for months to years, and their metabolic responses to both natural and anthropogenic perturbations.