The co-presence of polystyrene nanoplastics and ofloxacin demonstrates combined effects on structure, assembly, and metabolic activities of marine microbial community

Background: Nanoplastics (NP) is one of the most wide-spread and hazardous litter and can adsorb organic pollutants (e.g., antibiotics) and heavy metals, which may aggravate toxic effects on various organisms. Ofloxacin (OFL) is a common-used antibiotics that dramatically increased in environments. The combined effects of NP and OFL on planktonic/benthic microbial community structures, assembly, networks, and the shifts in prokaryotic metabolic activities, are still largely unknown. In this study, polystyrene NP and OFL, each with two concentrations, were combined into four treatments to investigate their joint effects on planktonic/benthic microbial communities. Multivariate analyses were conducted, while community assembly, co-occurrence networks, and prediction of prokaryotic pathways were analyzed. Results: (1) OFL and NP have impacts on planktonic/benthic communities of prokaryotes, while eukaryotic communities are more resistant to the adverse effects of OFL and NP; (2) planktonic/benthic communities of prokaryotes have better fit to the neutral community model (NCM) than those of eukaryotes do; benthic communities have wider niche breadths and better fit to NCM, indicating they are strongly influenced by stochastic processes; (3) the increase of OFL mainly reduces the numbers of nodes/edges of co-occurrence networks, implying the decrease of network complexity, while the increase of NP centralizes the nodes to fewer modules; the network fragmentation of planktonic communities is clearly higher than that of benthic communities, and OFL shows greater impacts than NP does; (4) the increase of NP under high OFL concentration is more likely to induce differential prokaryotic pathways in planktonic community; pathways in benthic community are less influenced. Conclusions: The present work indicates that the co-presence of NP and OFL has combined toxic effects on multiple aspects of planktonic/benthic microbial communities. NP and OFL have effects on prokaryotic community structures and component abundance, while the effects are limited in eukaryotic ones. The combined effects also include shrinking of niche breadths, simplifying of co-occurrence networks, and inducing of differential prokaryotic pathways. The current study suggests that the increasing NP in various environments, and the combined impacts with other pollutions, should be paid with more concerns. The detection, regulation, and elimination methods for NP are urgently needed.