Gut microbiome play a crucial role in geographical and interspecies variations in mercury accumulation by fish.

Mercury (Hg) contamination in fish has raised global concerns for decades. The Hg biotransformation can be manipulated by gut microbiome and it is found to have a substantial impact on the speciation and final fate of Hg in fish. However, the contribution of intestinal microbiota in geographical and interspecies variations in fish Hg levels has not been thoroughly understood. The present study compared the Hg levels in wild marine fish captured from two distinct regions in South China sea. We observed a quite "ironic" phenomenon that MeHg levels in carnivorous fish from a region with minimal human impacts (Xisha Islands, 92 ± 7.2 ng g-1 FW) were much higher than those from a region with severe human impacts (Daya Bay, 19 ± 0.41 ng g-1 FW). Furthermore, the results showed that gut microbiome determined Hg biotransformation and played a crucial role in the variances in fish Hg levels across different geographical locations and species. The intestinal methylators, rather than demethylators, were more significant in affecting Hg biotransformation in fish. The carnivorous species in Xisha Islands exhibited a higher abundance of intestinal methylators, leading to higher MeHg accumulation. Besides, the gut microbiome could be shaped in response to the elevated Hg levels in these fish, which may benefit their adaptation to Hg toxicity and overall health preservation. However, anthropogenic activities (particularly overfishing) in Daya Bay have severely affected the fish population, disrupting the reciprocal relationships between fish and intestinal microbiota and rendering them more susceptible to pathogenic microbes. Overall, this study provided a comprehensive understanding of the role of gut microbiome in Hg bioaccumulation in fish and offered valuable insights into the co-evolutionary dynamics between fish and gut microbiome in the presence of Hg exposure.

Effects of diet composition on gut microbiome and mercury biotransformation in the gobyfish.

Mercury (Hg) biotransformation (methylation and demethylation) could play a key role in affecting the final Hg speciation and level in fish. The gut microbiota was identified to be involved in this process. Diet is recognized to greatly influence the gut microbiome, whereas the impact of food composition on Hg biotransformation in fish has yet to be addressed. The study investigated the biotransformation and bioaccumulation of Hg in the gobyfish (Mugilogobius chulae) under different food choices (natural prey and artificial food) and evaluated the role of gut microbiome in these processes. The results showed that different diet composition significantly affected the gut microbiome and subsequently resulted in varied phenomenon of Hg biotransformation within fish body. Significant demethylation (0.33 % d-1) was only observed in the natural prey (brine shrimp) treatment, whereas methylation was occurred extremely slowly (0.013 % d-1) only in the artificial food (commercial dry pellets) treatment. Furthermore, the growth of demethylators was also enhanced in the natural prey treatment, which contributed to the demethylation process in fish. Furthermore, the gut microbial structure of gobyfish was greatly altered by different diet composition. This study highlights the significance of food choices in the minimization of Hg contamination in aquaculture. Incorporating natural prey into fish diets could be a better choice to balance the fish production and control MeHg levels. CAPSULE: Diet composition greatly affects the gut microbial composition, and natural prey could help to reduce the potential of MeHg accumulation by fish.

Antibiotic application may raise the potential of methylmercury accumulation in fish.

Mercury (Hg) biotransformation can significantly affect the Hg speciation and bioaccumulation in fish, where gut microbiota play an important role in this process. Antibiotics have been extensively used in aquaculture and can affect gut microbial structure. However, the influence of antibiotics on Hg biotransformation in fish has not been thoroughly understood. The present study investigated the effects of antibiotic (florfenicol) application on gut microbiota and subsequent impacts on Hg biotransformation and bioaccumulation in tilapia (Oreochromis mossambicus). The results showed that the florfenicol treatment did not affect IHg accumulation in the IHg-exposed fish or the MeHg accumulation in the MeHg-exposed fish. However, methylation was significantly weakened (from 0.015% d-1 to 0.005% d-1) and demethylation was completely terminated (from 0.046% d-1 to non-observable level) in the florfenicol-treated fish as compared to the control fish. This can be ascribed to the major shift in the richness of microbial methylators/demethylators in fish gut. Furthermore, florfenicol disturbed the homeostasis of gut microbiome and enhanced the growth of opportunistic pathogens. Our results strongly suggested that antibiotic application significantly altered the gut microbial community, thereby increasing the potential of MeHg accumulation by fish. This study highlights the importance of appropriate use of antibiotics in aquaculture as well as decreasing the environmental risks of Hg contamination in fish.

Clinical value of spectral CT in diagnosis of negative gallstones and common bile duct stones.

OBJECTIVE: To investigate the clinical value of spectral CT in diagnosis of negative gallstones and common bile duct stones primarily. METHODS: All patients diagnosed with negative biliary stones were analyzed and examined by spectral CT scanner retrospectively. Based on acquired raw imaging data, image series were reconstructed as described below: the optimal contrast-to-noise ratio monochromatic energy images, calcium- and fat- based material decomposition images and spectral curve images. All these imaging series were analyzed quantitatively and qualitatively. RESULTS: The contrast between negative stones and adjacent bile was 6.87 ± 5.48 HU on hybrid energy CT images and 47.30 ± 24.05 HU on optimal monochromatic energy CT images. The mean concentration of calcium in bile and negative stones was 19.36 ± 5.12 and 3.88 ± 6.60 mg/mL, and the fat in bile and negative stones was 998.48 ± 11.79 and 1035.68 ± 15.36 mg/mL. Effective atomic number Z of negative stones (6.60 ± 0.45) was lower than that of bile (7.65 ± 0.13). The slopes of the spectral curves for negative stones were k 90-40KeV = 1.43 ± 0.63 and k 140-90KeV = 0.19 ± 0.08, and for bile, they were k 90-40KeV = -0.27 ± 0.09 and k 140-90KeV = -0.04 ± 0.01. The same stone showed different densities in different imaging groups. The positive rate of conventional CT images was lower than that of other imaging groups. CONCLUSION: Spectral CT has a high diagnostic value for negative gallstones or bile duct stones, and material decomposition CT images and spectral curves can make an accurate diagnosis.