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Zoo gut plastispheres enable pathogen escape and adaptation
Summary
Zoo animals that are fed by humans, like tigers and elephants, had way more microplastics in their gut than wild animals, and these plastic bits were coated with harmful bacteria carrying antibiotic-resistance genes. Even more concerning, when these plastic-bacteria clusters were tested in water, they survived longer than bacteria not attached to plastic, meaning they could spread disease-causing microbes and antibiotic resistance further into the environment. This matters because it suggests microplastics may act as rafts that help dangerous bacteria persist and travel, a risk that likely isn't limited to zoo animals.
In zoos, intensive human contact and artificial feeding may create pathways for microplastic (MP) ingestion and gut colonization. We hypothesized that ingested MPs form intestinal plastispheres with elevated pathogenic potential and enhanced environmental persistence. To test this, we surveyed feces from 15 zoo-dwelling species and coupled particle characterization, feces-derived intestinal simulations, metagenomic sequencing, and a subsequent water-exposure experiment. Zoo feces contained more abundant MPs than reported for wild counterparts, with fragments predominating and polyethylene terephthalate (PET)/polystyrene (PS) dominating polymer profiles. MP burdens tracked human-animal interaction patterns, with human-fed species (e.g., Tiger, Elephant) carrying the highest loads (88-212 items/g). MPs supported dense biofilms whose composition diverged from bulk gut communities, exhibiting greater compositional variability and substrate-specific assembly. Metagenomic analyses revealed coordinated enrichment of potentially pathogenic taxa, virulence factor genes (VFGs), and antibiotic resistance genes (ARGs), with ARG profiles dominated by efflux- and inactivation-related mechanisms and tightly associated with mobile genetic elements. Elevated Type II/III/IV/VI secretion systems and effector delivery-related VFGs occurred within extracellular polymeric substance-rich biofilms, suggesting enhanced potential for ARG retention and horizontal gene transfer. During the 35-day aquatic exposure, MP-associated communities persisted longer than non-plastic particle-associated communities and free gut microbiota, suggesting that plastic-specific properties promote microbial persistence. PET/PS plastispheres showed the slowest declines in bacterial activity and favored the persistence of Enterococcus, Enterobacter, and Clostridium. Overall, intestinal MPs in zoo animals may select, enrich, and export high-risk microbiomes, highlighting the need for MP mitigation and evidence-based management of zoos and adjacent ecosystems.