Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
Environ Pollut
2023 Jul 01;328:121634. doi: 10.1016/j.envpol.2023.121634.
Show Gene links
Show Anatomy links
Size matters either way: Differently-sized microplastics affect amphibian host and symbiotic microbiota discriminately.
Zhang Q
,
Lv Y
,
Liu J
,
Chang L
,
Chen Q
,
Zhu L
,
Wang B
,
Jiang J
,
Zhu W
.
???displayArticle.abstract???
Concerns about the implications of microplastics (MPs) on aqueous animals have gained widespread attention. It has been postulated that the magnitude of MPs can influence its toxicity. However, little is known about how MPs toxicity changes with particle size. Amphibians are reliable bioindicators of ecosystem health due to their complex life cycles. In this study, we compared the influences of two sizes nonfunctionalized polystyrene microspheres (1 and 10 μm) on the metamorphosis of Asiatic toad (Bufo gargarizans). Acute exposure to MPs at high concentrations led to bioaccumulation in the digestive track and internal organs (i.e., liver and heart) of tadpoles. Long-term exposure to either size, at environmentally-related concentrations (1 and 4550 p/mL), led to growth and development delay in pro-metamorphic tadpoles. Remarkably, developmental plasticity mitigated these deleterious effects prior to the onset of metamorphic climax without compromising survival rate in later stages. MPs with a diameter of 10 μm dramatically altered the gut microbiota (e.g., abundance of Catabacter and Desulfovibrio) of pro-metamorphic tadpoles, whereas MPs with a diameter of 1 μm induced much more intensive transcriptional responses in the host tissues (e.g., upregulation of protein synthesis and mitochondrial energy metabolism, and downregulation of neural functions and cellular responses). Given that the two MPs sizes induced similar toxic outcomes, this suggests that their principal toxicity mechanisms are distinct. Small-sized MPs can travel easily across the intestinal mucosa and cause direct toxicity, while large-sized MPs accumulate in gut and affect the host by changing the homeostasis of digestive track. In conclusion, our findings indicate that MPs can affect the growth and development of amphibian larvae, but their developmental plasticity determines the ultimate detrimental effects. Multiple pathways of toxicity may contribute to the size-dependent toxicity of MPs. We anticipate that these findings will increase our understanding of the ecological effects of MPs.
Fig. 1. Accumulation of MPs in the tadpole digestive tract and internal organs after exposure to 2.275 × 106 p/mL 10 μm MPs for 12 h. The MPs in tissues are highlighted by red boxes. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Fig. 2. Influences of MPs exposure on tadpole development and growth. (a) Tadpole developmental stages after three weeks of treatment. Different letters denote significant intergroup differences in the proportions of a given stage (p < 0.05, χ2 test followed by Z test). (b–f) Intergroup differences in body weight (b), total length (c), body weight without gut (d), snout-vent length (e), and body condition score (f) after three weeks of treatment. Each bar stands for mean ± SE, and different letters denote significant differences between groups (p < 0.05, one-way ANOVA and S–N–K post hoc test). (g) Body weight when tadpoles reach to their stage 42 (onset of metamorphic climax). (h–i) Cumulative curves presenting the proportions of tadpoles reaching their stage 42 and stage 46 in a timeline. Asterisks denote significant intergroup differences in proportions of tadpoles reaching stage 42 or stage 46 at a given time (one-way ANOVA). (j–k) Dot plots and fitted curves presenting the proportions of tadpoles reaching their stage 42 and stage 46 at each day. Asterisks denote significant intergroup differences in proportions of tadpoles reaching stage 42 or stage 46 at a given day (p < 0.05, χ2 test followed by Z test).
Fig. 3. Influences of MPs on the bacterial diversity in the digestive tract of B. gargarizans tadpoles. (a) Relative amount of gut bacteria based on qPCR. The data was analyzed with Kruskal-Wallis test. (b) Bacterial composition at phylum level. (c) Variations in alpha-diversity indices between groups. Each bar stands for mean ± SE (n = 6), and different letters denote significant differences between groups. (d–e) PCoA scatter plots presenting the variations in beta-diversity based on unweighted UniFrac (d) and weighted UniFrac (e) distances.
Fig. 4. Differential analyses on the gut microbial abundance and function. (a) Heatmap presenting the bacterial taxa varied significantly across groups (q < 0.05, Kruskal-Wallis test and BH correction). The color of the tiles denotes the relative abundance (in percentages). The asterisks in the right columns denote the differential bacterial taxa based on LEfSe (detailed in Fig. S7). (b) Influences of MPs on bacterial functions in the tadpole gut. The asterisks denote significant influences of 1 or 10 μm MPs on microbial abundances (Kruskal-Wallis tests on the blank, low, and high concentration groups for each sized MPs). (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Fig. 5. Influences of MPs on the transcriptional profile of tadpole tissues. (a) PCoA scatter plot presenting the similarity in transcriptional profile of samples. (b) Venn plot presenting the DEGs (q < 0.05, DESeq2 and BH correction) of pairwise comparisons. Note that 1 μm MPs cause much more DEGs than 10 μm MPs. (c) Heatmap presenting the variation trends of the DEGs. (d) Volcano map presenting the variation degree of all the identified genes. Each point denotes one gene. Genes varied dramatically (fold change >200 and q < 0.05) are colored in red and labeled with their annotations. Note the top four genes which show the highest fold changes (MSTRG_7420, MSTRG_34,994, MSTRG_2609, and MSTRG_43,556) are shared by the 1 and 10 μm MPs treatment groups, and they are highlighted with red labels. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Fig. 6. Functional enrichment analysis of DEGs. (a–d) Functional enrichment of DEGs caused by 1 μm MPs groups: a–b, GO enrichment; c–d, KEGG enrichment. (a and c) Dot plot representing the top 20 significantly enriched items. The cover rate is the ratio of enriched DEGs number to the total gene number of a given pathway. (b and d) Networks presenting the relationships between the enriched items and the variation patterns of the DEGs. Each small note denotes one DEG, and each large note denotes one functional item. The size of the nodes for functional items denotes the numbers of enriched DEGs, while the color of the nodes for DEGs denotes fold change. (e–f) Results of functional enrichment based on DEGs caused by 10 μm MPs. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)
Fig. 7. A schematic diagram summarizing the influences of polystyrene MPs on tadpoles and the underlying toxicological pathways.