Different recovery patterns of the surviving bivalve Mytilus galloprovincialis based on transcriptome profiling exposed to spherical or fibrous polyethylene microplastics

Abstract

Microplastics (MPs) are pervasive pollutants exuded from anthropogenic activities and ingested by animals in different ecosystems. This transcriptomic profiling study aimed to explore the impact of polyethylene MPs on Mytilus galloprovincialis, an ecologically significant bivalve species. The toxicity of two MPs types was found to result in increased cellular stress when exposed up to 14 days. Moreover, recovery mechanisms were also observed in progress. Mussels exhibited different gene expression patterns and molecular regulation in response to cellular reactive oxygen species (ROS) stress. The transcriptome analysis demonstrated a notable hindrance in cilia movement as MPs ingested through gills. Subsequent entry resulted in a significant disruption in the cytoskeletal organization, cellular projection, and cilia beat frequency. On day 4 (D4), signal transduction and activation of apoptosis evidenced the signs of toxic consequences. Mussels exposed to spherical MPs shown significant recovery on day 14 (D14), characterized by the upregulation of anti-apoptotic genes and antioxidant genes. The expression of P53 and BCL2 genes was pivotal in controlling the apoptotic process and promoting cell survival. Mussels exposed to fibrous MPs displayed a delayed cell survival effect. However, the elevated physiological stress due to fibrous MPs resulted in energy transfer by compensatory regulation of metabolic processes to expedite cellular recovery. These observations highlighted the intricate and varied reaction of cell survival mechanisms in mussels to recover toxicity. This study provides critical evidence of the ecotoxicological impacts of two different MPs and emphasizes the environmental risks they pose to aquatic ecosystems. Our conclusion highlights the detrimental effects of MPs on M. galloprovincialis and the need for more stringent regulations to protect marine ecosystems.

Keywords: Ecotoxicity; Environmental pollution; Microplastics; RNA-Seq; Transcriptomics.

Fig. 1

Transcriptome DEGs of the MPs treatment group represents the GO categories and overall functional annotation.

Fig. 2

Venn diagram showing the significant unique and shared DEGs between compared treatment groups and control. Regulated gene sets related (a) within sphere treatment groups vs. control. (b) A cnet plot of gene sets (P < 0.05, FDR <0.05) networking the biological processes. (c) within fiber treatment groups vs. control. (d) A cnet plot of gene sets (P < 0.05, FDR <0.05) networking the biological processes.

Fig. 3

Venn diagram shows the number of significant DEGs on MPs exposure for up to 14 days. Gene sets related to treatment groups vs. control and between treatment groups; the bar diagram represents the biological processes corresponding to different GO classes.

Fig. 4

(a) GO analysis of genes differentially expressed indicates the activated and suppressed biological processes in mussels exposed to spherical MPs. (b) GO analysis of genes differentially expressed shows the activated and suppressed biological processes in mussels exposed to fiber MPs. (c) KEGG analysis of DEGs indicates the activated and suppressed biological processes in the spherical MPs treatment group. (d) KEGG analysis of DEGs shows the activated and suppressed biological processes in the fiber MPs treatment group.

Fig. 5

(a) Heatmap shows the relative expression of the significant genes in the treatment groups; (b) Schematic representation of biological responses in the treatment groups exposed to varying spherical and fibrous MPs concentrations. Mitochondrial impairment results in the ROS generation and regulation of caspase-dependent and caspase-independent apoptosis; accumulated ROS increases oxidative damages and downregulated cytoprotective genes; molecular regulation of stress response proteins controls apoptosis, DNA repair and regulate gene transcription to initiate survival responses and recovery.

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