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Distinct riverine plastispheres and microplastic-specific community complexity in the near-bottom benthic habitat under natural hydrological conditions
Summary
Scientists found that different types of plastic litter sitting at the bottom of rivers each grow their own unique community of microbes, sort of like tiny biofilm "neighborhoods" that vary by plastic type. Interestingly, so-called "biodegradable" plastics (PLA and PHA) hosted different microbes than regular plastics like PET and PVC, including some that support nitrogen cycling in the environment — but this doesn't necessarily mean they break down faster or safer. This matters because these microbial communities can affect how quickly plastics degrade, potentially into smaller microplastic particles that end up in water we drink and
Aquatic near-bottom benthic habitats are important retention zones for waterborne microplastics (MPs), yet the assembly and ecological traits of the benthic plastisphere remain understudied, particularly how prevalent polymers regulate succession and micro-ecological processes. Here, five representative MPs, including polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polylactic acid (PLA), and polyhydroxyalkanoates (PHA), were incubated for 100 days in an urban river's near-bottom benthic habitat. Bacterial, archaeal, and eukaryotic communities were characterized using DNA- and RNA-based amplicon sequencing, together with community assembly, co-occurrence network, functional prediction, and surface-aging analyses. Mature plastispheres formed distinct niches relative to ambient water and sediment communities. Although stochastic processes generally dominated community assembly, rainfall-associated hydrological disturbance increased deterministic contributions without eliminating polymer-specific signatures. MP-specific community complexity was reflected in substrate-dependent assemblages, network topology, RNA-resolved active keystone taxa, and predicted functional potential. Biodegradable PLA and PHA supported communities distinct from traditional non-biodegradable MPs and enriched nitrogen-cycling traits. PET represented an exceptional non-biodegradable polymer, showing a unique successional trajectory, pronounced surface-aging signals, and highly connected networks, suggesting broader microbial interactions at the polymer-biofilm interface. RNA-based sequencing uncovered a prominent role of active eukaryotes in network interactions, a pattern undetected by DNA-based profiling. Comamonadaceae, Rhodocyclaceae, Saprospiraceae, and Bacillariophyceae were identified as candidate taxa potentially associated with polymer surface aging and degradation-related processes based on co-occurrence network and enrichment analyses. This study provides field-based micro-ecological insights into plastisphere assembly in freshwater near-bottom benthic habitats under natural hydrological conditions and identifies key microbial taxa and functions linked to MP fate.