| As the quick development of nanotechnology, nanomaterials is enteringthe environment with a increasing pace, through their usage in industry, agriculture, medicine, food, and etc. In the environment, these new materials will inevitablly interact with other contaminants, such as persistant organic pollutants(POPs), and thus affect the transportation, bioavailability, and toxicity of the contaminants. However, the interactive process of nanomaterials, such as carbon nano tubues, on POPs, are not well understand yet. Pentachlorophenol (PCP) has been widely used to control oncomelania, the intermediate hosts of schistosomes, in the middle and lower reaches of Yangtze River since the 1950s, which resulted in different levels of fishery water pollution and threat the healthy growth of fishes, even caused a large number of deaths. In this study, we aimed to investigate the effect of carboxylated multi-walled carbon nanotubes (MWCNT-COOH)on the bioacculation of PCP in fish. From the perspective of microbial ecology with a new generation of high-throughput sequencing technology (454 sequencing technology), the effect of PCP and MWCNT-COOH onthe the structure and composition of intestinal floraon goldfish(Carassius auratus)was studedThe relationship between the structure of intestinal flora and changes of goldfish growth phenotype was analyzed.Results and conclusions were summarized as following:1) The effect of MWCNT-COOH on the bioaccumulation of PCP in goldfish(Carassius auratus) were studied with different concentration of PCP (50 μg/L, 100 μg/L) with the coexistence of MWCNT-COOH(100 μg/L) in a 50 d exposure period followed by a 14-d depuration period. It was found that before reached a pseudosteady-state, PCP concentrations in fish exposed to PCP alonewere was higher than that with the coexistence of MWCNT-COOH (100 μg/L). In addition PCP concentration in the gills and gut content were significantly higher than that in muscle. It is interesting to find that in the depuration phase the PCP concentrations of all tissues with the coexistence of MWCNT-COOH were significantly higher than that of PCP exposure alone. The extra PCP might be from the MWCNT-COOH-bound PCP that accumulated in the digestive track indicating the release of PCP from MWCNT-COOH in fish.2)The activity of SOD and CAT in goldfishlivers was significantly influenced by PCPexposure. At the short-term exposure, the activity of SOD and CAT reduced first, and increased then in low dose, whereasthe activity of SOD and CAT decreased in high dose. Histopathological observation showed that 14-d exposure to PCP at 10 μg/L induced multifocal inflammation, cell swelling and cytoplasmic vacuolization in livers. Focal necrosis, a very severe and irreversible type of damage, appeared in high frequency in 100 μg/L exposure group. PCP exposure was also found to induce aneurisms, oedema and epithelial lifting in gill. Thus, PCP is an extreme toxicant to the fish. For MWCNT-COOH exposure,the results demonstrated that the antioxidant enzymes SOD and CAT were inhibited significantlyin the liver of goldfishexposed to 100 μg/L and 1000 μg/L MWCNT-COOH for 28 d. Exposure to MWCNT-COOH resulted in the increaseof the incidence of oedema in the secondary lamellae, aneurisms and hyperplasia in the primary lamellae. MWCNT-COOH exposure was also found to induce necrosis and vacuolization in liver at the high dose of 100μg/L. However, There were no changes at the low MWCNT-COOH exposure level (dose of 10μg/L)in liver compared to control.MWCNT-COOHis a low toxic material to goldfish.For the join exposure of PCP andMWCNT-COOH,SOD reduced first, and increased then in low dose, whereasthe activity of CAT was strongly inhibited when the exposure dose reached 100μg/L.The exposure with the coexistence of both PCP and MWCNT-COOH resulted in the increase of the incidence of oedema in the secondary lamellae,aneurisms and hyperplasia in the primary lamellae in all dose. There were no changes at the low dose in liver.The coexistence of MWNT-COOH seems reduced the toxicity of pentachlorophenol.3)The correlations of fish gut microbial community shift with the induced toxicological effects were studied with Goldfish (Carassius auratus) exposed to 0-100 μg/L PCP for 28 d. PCP exposure caused accumulation of PCP in fish intestinal tract in a time and dose-dependent manner, andthe maximum level of PCP was observed in hepatic tissue after 21-d exposure. Under the relatively higher PCP stress, fish body weight and liver weight were reduced, and the hepatic CAT and SOD activities were inhibited, demonstrating negative correlations with the PCP levels in liver and gut (R<-0.5, P< 0.05 each). Pyrosequencing of 16S rRNA genes indicated that PCP exposure increased the Bacteroidetes abundance and decreased the Firmicutes abundance in fish gut. Within Bacteroidetes phylum, Bacteroides genus had the highest abundance, which was significantly correlated with PCP exposure dosage and duration (R> 0.5, P < 0.05 each). Bioinformatic analysis revealed that Bacteroides showed quantitatively negative correlations with Chryseobacterium, Microbacerium, Arthrobacter and Legionella in fish gut, and Bacteroidetes abundance, Bacteroides abundance, and Firmicutes/Bacteroidetes ratio played crucial roles in the reduction of body weight and liver weight under PCP stress. The results may extend our knowledge regarding the roles of gut microbiotain ecotoxicology.4)The correlations of fish gut microbial community shift with the induced toxicological effects were also studied with Goldfish (Carassius auratus) exposed to MWCNT-COOH for 28 d. Oxidative damage and appearance of adverse liver and gill lesions could be found by MWCNT-COOH exposure. With the increaseof exposure time, the relative abundance of Bacteroidetes andBacteroides increased, and the relative abundance of Firmicutes decreased. The Firmicutes/Bacteroidetes ratio (F/B) significantly decreased with the increase of the exposure period to MWCNT-COOH.Liver weight (R2=0.3512, p=0.01)and body weight (R2=0.3027, p=0.02)were positively correlated with the Firmicutes/Bacteroidetes ratio (F/B) (R2 =0.4344, p< 0.01) (Fig.3,S7a). Liver weightwas negatively correlated with the Bacteroidetes (R2= 0.511, p= 0.001) phylum and Bacteroides (R2= 0.5271, p= 0.0009) genus, and body weight was negatively correlated with the Bacteroidetes (R2 = 0.4485, p= 0.003) phylum and Bacteroides (R2= 0.4422, p= 0.003) genus.The body weight andliver weight of the fish decreased significantly (p< 0.05) after exposure to MWNT-COOH/aq for 28 d, indicating that MWCNT-COOH/aq had an inhibitory effect on the fish growth. MWNT-COOH inducedprofound metabolic changes by modulating the composition and the activity of the intestinal microbiota, which can affect the fish healthy and the function of digestive system. |
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