Bioavailability of trace metals to marine bivalves mediated by dissolved and colloidal organic carbon

The significant roles of colloidal nanoparticles or macromolecules in the biogeochemical cycling of trace metals and thus the interaction between organic matter and trace metals in aquatic environments have been demonstrated recently. In this study laboratory experiments employing radiotracer methodology and ultrafiltration techniques were conducted to examine the influences of natural dissolved organic carbon (DOC) and colloidal organic carbon (COC) on the bioavailability of trace metals (Fe, Cr, Ag, Cd, and Hg in forms of inorganic and methylated) to the green mussel Perna viridis (and the clam Ruditapes philippinarum for Cr and Fe) at different concentrations of DOC and COC from different origins (estuarine, coastal, and diatom decomposed). The differential utilizations of organic carbon by the marine mussels through the assimilation of five phytoplankton diets and from the dissolved phase were also investigated. Standard compounds (glucose, amino acids arginine and leucine, and high molecular weight carbohydrate particles with size ranging from 3 to 2000 kDa) were used to study the organic matter flux into the green mussel P. viridis. The results demonstrated that natural colloid-bound metals were bioavailable to the green mussels and clams. The influences of COC on metal bioavailability were metal-specific and dependent on the geochemical properties of colloids and colloid-metal complexation. Using the DOC originating from the decomposed diatom (Thalassiosira pseudonana), I demonstrated that Cd and Cr uptake increased linearly with increasing DOC concentration. While this biogenic DOC decreased the uptake of Hg(II). The bioavailability of MeHg was weakly influenced by different DOC quality or quantity. Results demonstrated the direct accumulation of biogenic DOC obtained from the diatom decomposition, and the significant utilization of COC as nutrients of the mussels. A variety of HMW dextrans (at substrate concentrations of 0.2 to 2 mg L-1) were actively ingested by the mussels. A kinetic model was applied to quantitatively evaluate the carbon contribution from the dissolved and particulate sources to the general organic carbon utilization of the mussels. It appears that the mussels were able to utilize colloids of different sizes, thus playing an important role in the cycling of DOC in the coastal waters

Protocol to retrieve unknown flanking DNA sequences using semi-site-specific PCR-based genome walking

Summary: Here, we describe a protocol based on semi-site-specific primer PCR (3SP-PCR) to access unknown flanking DNA sequences. We specify the guidelines for designing primers for 3SP-PCR. We also describe experimental procedures for the 3SP-PCR, along with PCR product purification and subsequent sequencing and analysis.For complete details on the use and execution of this protocol, please refer to Wei et al.1 : Publisher’s note: Undertaking any experimental protocol requires adherence to local institutional guidelines for laboratory safety and ethics

New insights into the mechanism of ammonia toxicity: Focus on Cactus

The NF-κB signaling pathway is the most critical pathway in innate immunity. IκB (Cactus) is the primary cytoplasmic inhibitor of NF-κB (Dorsal). In this study, we found that ammonia exposure could significantly induce the expression of Cactus, in a dose-dependent manner in different tissues, with the highest expression in the gill of Corbicula fluminea. The expression pattern-related elements (Tube and Dorsal) in the NF-κB signaling pathway were also analyzed, showing significant up-regulation in 48 h. There was an inhibitory effect between up-regulated Cactus and Dorsal in 72 h, which may regulate Dorsal as a negative feedback pathway function to control the expression of pro-inflammatory cytokines (IL-1β, IL-6, and TNF-α). Besides, through molecular docking simulation, we found that the Cactus could be directly activated by NH3, complementing the regulatory mechanism of the Cactus. To further test our hypothesis, the levels of pro-inflammatory cytokines decreased after adding PDTC (the antioxidant of Cactus/IκB), suggesting that PDTC can prevent the degradation of Cactus, inhibit Dorsal translocating into the nucleus, and activate the pro-inflammatory cytokines. This revealed the inhibitory effect of Cactus on activating Dorsal/NF-κB factors in the NF-κB signaling pathway. Thus, we suggested that the Cactus is an essential regulator of ammonia-activated inflammation in C. fluminea, which was reported to be activated only by bacteria and immune stimulators. Our study provides a new perspective on the mechanism of ammonia toxicity in invertebrates