Microplastic contamination alters microbial community in commercially important bivalves, Geloina expansa, Anadara cornea, and Meretrix meretrix from tropical waters.

Microplastics pose serious risks for aquatic organisms such as fishes, shrimps and bivalves. Bivalves are particularly vulnerable due to their filter-feeding strategy and sedentary life. While the microplastic bioaccumulation in bivalves has been well documented, the effects of microplastics accumulation on bivalve's gut microbiome in tropical sea waters remains poorly understood. To fill this knowledge gap, a 10-day feeding experiment with 13 mg L-1 polyethylene terephthalate particles was conducted using three commercially important bivalve species: Anadara cornea, Geloina expansa, and Meretrix meretrix taken from two contrasting locations (brackish water in protected Setiu Wetlands compared to open water in Kertih River) to investigate the effect of microplastic pollution on diversity and composition of gut prokaryotes using 16S rRNA amplicon sequencing. The results showed that alpha diversity of gut prokaryotes differed among species after microplastic exposure. For example, microplastic exposure increased operational taxonomic units (OTUs) richness of gut prokaryotes in G. expansa compared to A. cornea and M. meretrix during 10-day treatment. Community structure of prokaryotic community in bivalves gut showed strong divergence between Setiu Wetlands and Kertih River. Significant effects of microplastic exposure on relative abundance of prokaryotic phyla were also observed. Gut microbiome of G. expansa showed increase of relative abundance of Archaea and Firmicutes after microplastic exposure. The results suggest that microplastic treatment promotes dominance of certain bacterial species, likely those with plastic-metabolizing capabilities, potentially boosting bivalve resilience to microplastic contamination.