Changes in dysbiosis and gene expression in the gut of wharf roach (Ligia spp.) fed with expanded polystyrene

The East Asian region, with its intensive human and fishery activity, suffers from serious marine plastic pollution along its coastlines. Wharf roaches (Ligia spp.) on the coast of western Japan frequently ingest expanded polystyrene (EPS) and excrete it as microplastic in their feces, yet the effects on their gut remain unclear. Under controlled laboratory exposure, we examined both the host gut transcriptome, and the gut microbiome of wharf roaches fed EPS versus a fasted control group. DESeq2 and PyDESeq2 yielded a high-confidence set of 25 differentially expressed genes, among which xenobiotic-metabolism enzymes-a cytochrome P450, a UDP-glucuronosyltransferase, and a sulfotransferase-were up-regulated in the EPS-fed group. In contrast, the overall gut microbial community structure was unchanged: neither alpha nor beta diversity differed significantly between groups in any domain. At the taxon level, a few low-abundance archaeal and viral taxa, including the archaea Methanospirillum, Halalkalicoccus, and Desulfurococcus, and T4-like viruses, were detected in all EPS samples but were below the detection limit in all controls. Because the comparison used a fasted control, the extent to which these responses are specific to EPS exposure remains to be established. Building on previous field studies identifying wharf roaches as bioindicators of coastal EPS pollution, this study highlights the wharf roach as a tractable model for investigating the gut-level effects of plastic ingestion.