Microbially mediated Fe-N coupled cycling at different hydrological regimes in riparian wetland.

Although the significance of the coupled Fe- and N- cycling processes on biogeochemical transformation in riparian wetlands is well-known, the regulation associated with the changes on the microbiotas during different hydrological regimes remains unclear. This study performed field investigations on the bacterial community compositions (BCC) and specific genera associated to Fe- and N- cycling in the rhizosphere soil and sediments in a riparian wetland in Poyang lake, China. The predominant phyla Proteobacteria, Acidobacteria, and Nitrospirae from all the samples remarkably decreased after long-term continuous flooding, while Actinobacteria, Firmicutes and Bacteroidetes were enriched. For the family level, the relative abundances of iron-oxidizing bacteria (FeOB) Gallionellaceae, and N fixing bacteria Nitrospiraceae and Bradyrhizobiaceae significantly declined upon the long-term flooding and then increased with dewatering, which were consistent with the functional genes sequencing analysis. In which, the Bradyrhizobiaceae (RA 2.0 %-34.6 %) was the dominant nirS denitrifier and potential iron-reducing bacteria (FeRB), Sideroxydans lithotrophicus was one of the dominant FeOB (RA 1.7 %-23 %), which was also identified to be the nirS dentrifier (RA 0.2 %-4.3 %). The absolute quantification of the functional genes levels including nirS, nirK, FeRB (Geobacter spp.) showed their significant increases by 3-7 times upon desiccation compared to that under post-CF. The PCA and RDA results indicated the linkage between redox changes of N and Fe during inundation mediated by FeRB, NOB, and FeOB, which were closely related to hydrochemical indices NO3-, Fe2+ and SO42-. These evidences all implied the likely occurrence of nitrate reduction coupled to Fe(II) oxidation (NRFeOx) under oligotrophic conditions, which was potentially facilitated by metabolizers consisting of highly correlated Bradyrhizobiaceae and Sideroxydans (rho = 0.86, p < 0.01). These findings provide an interpretation of the biological reactions in the microbially mediated NRFeOx processes driven by hydrological change, which could assist the mechanistic understanding of the global biogeochemical cycles of iron and nitrogen in riparian wetlands.

Toxicokinetics and toxic effects of a Chinese PFOS alternative F-53B in adult zebrafish.

6:2 chlorinated polyfluorinated ether sulfonate (F-53B), a Chinese PFOS alternative, has recently been identified in river water, sewage sludge, wildlife and humans, causing great concerns about its potential toxic effects. Here, we report the first investigation of the toxicokinetics and oxidative stress of F-53B in adult zebrafish. Adult male and female zebrafish were exposed to 10 and 100 µg/L of F-53B for 7 days followed by a 5-d depuration period to examine bioaccumulation, distribution, and depuration of F-53B in fish. The results showed that F-53B was readily accumulated in fish tissues with log BCF values of 2.36-3.65, but was eliminated slowly (t1/2 = 152.4-358.5 h). F-53B accumulation was greater in males than in females and the concentration in tissues decreased in the following order: gonad ≈ liver ≫ gill ≫ brain in females and liver ≈ gill ≫ gonad ≫ brain in males, showing sex- and tissue- specific accumulation of F-53B in fish. After chronic exposure to F-53B for 28 days, a significant dose-dependent increase in histopathological changes in the liver were mainly manifested by vacuolation. Furthermore, F-53B also significantly reduced the enzyme activity (or content) of most of the measured oxidative stress-related markers (e.g., SOD, CAT and MDA) except for an increase in GSH-Px activity, indicating that oxidative stress was induced in zebrafish after treatment with F-53B. The results of this study provide important information on the toxicokinetics and toxic effects of F-53B, which will contribute to the ecological risk assessments of F-53B released into surface waters.

Activation of Macrophages in vitro by Phospholipids from Brain of Katsuwonus pelamis (Skipjack Tuna).

The biological activities of phospholipids (PLs) have attracted people's attention, especially marine phospholipids with omega-3 polyunsaturated fatty acids DHA and EPA. In this study, we investigated the immunity activation of macrophages in vitro by phospholipids from skipjack brain. The phospholipids were extracted with hexane and ethanol ultrasonication instead of the traditional method of methanol and chloroform. The content of phospholipids from Skipjack brain was 19.59 g/kg by the method (the ratio of hexane and ethanol 2:1, 40 min, 35°C, 1:9 of the ratio of material to solvent, ultrasonic power 300W, ultrasonic extraction 2 times). The RAW264.7 macrophages were stimulated by the phospholipids from the Skipjack, by which the volume, viability and phagocytosis of macrophages were increased. The concentration of NO and the activity of SOD of the cells were also enhanced. The gene expressions of IL-1ß, IL-6, iNOS and TNF-α mRNA assayed by RT-PCR were up-regulated. Phospholipids from brain of Skipjack Tuna could activate macrophages immunity which displayed to induce pro-inflammatroy cytokines mRNA expression.