Polystyrene-degrading bacteria in the gut microbiome of marine benthic polychaetes support enhanced digestion of plastic fragments

Polystyrene foam, which is used as a buoyant material in mariculture, is a common constituent of marine plastic debris. Here, we conduct analyses on polystyrene foam debris collected on the east coast of Xiamen Island, China, and associated plastic-burrowing clamworms. We apply interferometry, mass spectrometry and microscopy to polystyrene foam fragments excreted by the benthic clamworms (Perinereis vancaurica). We find evidence of polystyrene digestion and degradation during passage of the clamworm gut leading to the formation and accumulation of microplastics, with a mean diameter of 0.6 ± 0.2 mm. 16S rRNA gene sequence analysis of clamworm intestines indicated diverse bacterial gut microbiome, dominated by Acinetobacter and Ruegeria bacteria. Further characterization confirmed that polystyrene was degraded by representative gut isolates of Acinetobacter johnsonii, Brevibacterium casei, and Ruegeria arenilitoris. During a 30-day incubation, we observed a very slight decrease in polystyrene weight, changes in chemical group and thermal characteristic, and production of polystyrene metabolic intermediates. Our findings indicate that polystyrene-degrading bacteria in the gut microbiome of clamworms may influence plastic fragmentation and degradation in marine ecosystems.