Biodegradation and disintegration of expanded polystyrene by sphaeromatid isopods Sphaeroma via their gut bacteria

Wood-boring isopods have been documented inhabiting the plastic floats of expanded polystyrene (EPS), which is extensively utilized in mariculture as buoyant material. However, little is known about their role in the plastic fragmentation and degradation. This report confirmed that globally distributed Sphaeroma gnawed and ingested EPS foam, and digested it via their gut microbiome. After 7 days of exposure, each Sphaeroma consumed 4.4 ± 0.2 mg EPS, ingested 50 microbeads and egested 2.5 ± 0.7 × 10³ microplastics. Analyses using μFTIR, GPC, and GC-MS revealed polystyrene (PS) degradation in the gut of Sphaeroma. High throughput 16S rRNA sequencing revealed that Exiguobacterium spp. and Brevibacterium spp. were associated with PS diets in the gut microbiome of Sphaeroma, suggesting their potential key role in vivo. Further characterizations of PS weight loss, changes in chemical and thermal properties, and identification of metabolic intermediates confirmed that PS can be degraded by five gut bacteria from the above two genera. Antibiotic bioassay confirmed that gut microbes are essential for the EPS depolymerization in Sphaeroma by. All these results demonstrate that the gut microbiome contributes to EPS digestion in the host. Together, these results found marine isopods in coastal negatively influenced the environmental fats of the plastic fate, by fragmenting plastics and generating microplastics, via their PS-degrading gut microbiota.