The neuropeptides of Asian freshwater clam (Corbicula fluminea) as new molecular biomarker basing on the responses of organophosphate chemicals exposure

Toxicity effects of ciprofloxacin on biochemical parameters, histological characteristics, and behaviors of Corbicula fluminea in different substrates

Antibiotic toxicity and antibiotic resistance have become significant challenges to human health. However, the potential ecotoxicity of sediment-associated antibiotics remains unknown. In this study, biochemical responses, histological changes, and behavioral responses of Corbicula fluminea exposed to sediment-associated ciprofloxacin (CIP) were systemically investigated. Special attention was paid to the influence of different substrate types. Biochemical analyses revealed that the balance of the antioxidant system was disrupted, eventually leading to oxidative damage to the gills and digestive gland with increasing CIP concentration. Severe histopathological changes appeared along with the oxidative damage. An enlargement of the tubule lumen and thinning of the epithelium in the digestive gland were observed under exposure to high CIP concentrations (0.5 and 2.5 μg/g CIP). In a behavioral assay, the filtration rate of C. fluminea in high concentration exposure groups was clearly inhibited. Moreover, from the integrated biomarker response (IBR) index, the toxicity response gradients of the digestive gland (no substrate--NOS > Sand > Sand and kaolinite clay-- SKC > Sand, kaolinite clay, and organic matter--SCO) and gills (NOS > SCO > SKC > Sand) were different among substrate exposure groups. The most serious histopathological damage and highest siphoning inhibition were observed in the NOS group. The changes in the morphological structure of digestive gland cells in C. fluminea were similar in the other three substrate groups. The inhibition of the filtration rate in the higher concentration groups decreased in the order Sand > SKC > SCO.

Responses of Asian clams (Corbicula fluminea) to low concentration cadmium stress: Whether the depuration phase restores physiological characteristics

The effect of low concentration Cd stress on bivalves is unclear. In this study, Asian clams (Corbicula fluminea) were continuously exposed to 0, 0.05, 0.10, and 0.20 mg/L Cd for 14 d (exposure phase) and to artificial freshwater for 7 d (depuration phase). A total of 16 variables were measured to explore the toxic effects on C. fluminea. All physiological characteristics were significantly inhibited in the treatments (p < 0.05), and the negative effects of Cd did not return to normal levels in the short term. Tissue damage was found in the feet and gills of C. fluminea in all the treatments. On the 7th day (D7), enzyme activity in all the treatments was significantly higher (p < 0.05) than in the control group. Acetylcholinesterase, superoxide dismutase, and catalase activities were enhanced on D14 in all the treatments. However, only glutathione S-transferase activity was significantly higher in all the treatments (p < 0.05) than in the control group on D21. The instability of the enzymes indicated that the adaptability of C. fluminea became stronger throughout the experiment. In each group, the maximum bioaccumulation of Cd followed the order: 0.20 mg/L > 0.05 mg/L > 0.10 mg/L, which might be caused by the filtration capacity of C. fluminea in the 0.05-mg/L group, which was higher than that of the 0.10-mg/L group. Thus, low Cd concentrations effect the physiological characteristics, tissue health, and antioxidant system of C. fluminea and may require a long recovery time to be restored to normal levels.

Development and Interrogation of a Transcriptomic Resource for the Giant Triton Snail (Charonia tritonis)

Gastropod molluscs are among the most abundant species that inhabit coral reef ecosystems. Many are specialist predators, along with the giant triton snail Charonia tritonis (Linnaeus, 1758) whose diet consists of Acanthaster planci (crown-of-thorns starfish), a corallivore known to consume enormous quantities of reef-building coral. C. tritonis are considered vulnerable due to overexploitation, and a decline in their populations is believed to have contributed to recurring A. planci population outbreaks. Aquaculture is considered one approach that could help restore natural populations of C. tritonis and mitigate coral loss; however, numerous questions remain unanswered regarding their life cycle, including the molecular factors that regulate their reproduction and development. In this study, we have established a reference C. tritonis transcriptome derived from developmental stages (embryo and veliger) and adult tissues. This was used to identify genes associated with cell signalling, such as neuropeptides and G protein-coupled receptors (GPCRs), involved in endocrine and olfactory signalling. A comparison of developmental stages showed that several neuropeptide precursors are exclusively expressed in post-hatch veligers and functional analysis found that FFamide stimulated a significant (20.3%) increase in larval heart rate. GPCRs unique to veligers, and a diversity of rhodopsin-like GPCRs located within adult cephalic tentacles, all represent candidate olfactory receptors. In addition, the cytochrome P450 superfamily, which participates in the biosynthesis and degradation of steroid hormones and lipids, was also found to be expanded with at least 91 genes annotated, mostly in gill tissue. These findings further progress our understanding of C. tritonis with possible application in developing aquaculture methods.

Characterization of the GABAergic system in Asian clam Corbicula fluminea: Phylogenetic analysis, tissue distribution, and response to the aquatic contaminant carbamazepine

Gamma-aminobutyric acid (GABA) is the major inhibitory neurotransmitter involved in the neuro-endocrine-immune (NEI) system. In this study, we sequenced the partial length of cDNA fragments of three genes involved in GABA neurotransmitter system of the Asian clam (Corbicula fluminea) (GABA_A receptor-associated protein (GABARAP), GABARAPL2 and GABA transporter (GAT-1)). These genes exhibited high amino acid sequence identity compared with other invertebrate orthologs. Expression patterns of the three genes were determined in mantle, gill, gonad, digestive gland and muscle, and the steady state levels of mRNA for each were determined to be highest in gonad and lowest in muscle. To determine their regulation by pharmaceuticals that are present as contaminants in waterways, clams were exposed to carbamazepine (CBZ) for 30 days. CBZ is an agonist for GABA receptors and is an anticonvulsant pharmaceutical that is often detected in aquatic ecosystems. GABARAP and GABARAPL2 mRNA levels were significantly downregulated by 5 and 50 μg/L CBZ in mantle and gill (p < 0.05), while in the gonad and digestive gland, steady state levels (p < 0.05) were decreased with exposure to all three doses. GAT-1 mRNA was upregulated by CBZ (p < 0.05) in the mantle and gill at all three doses tested and in the gonad and digestive system with 5 and 50 μg/L. These data suggest that CBZ disrupt the expression of the GABAergic neurotransmitter system in C. fluminea. Moreover, GABARAP, GABARAPL2 and GAT-1 may be useful biomarkers for the screening of substances that are hazardous to the NEI system of mollusks.

ROS changes are responsible for tributyl phosphate (TBP)-induced toxicity in the alga Phaeodactylum tricornutum

As a newly emerging environmental contaminant, tributyl phosphate (TBP) is an additive flame retardant of high production volume that is frequently detected in biota and the environment. Despite evidence that TBP is a potential threat to marine organisms, ecotoxicology data for TBP in marine organisms at low trophic levels are scarce. In this study, the acute toxicological effect of TBP on the marine phytoplankton Phaeodactylum tricornutum was thoroughly investigated, and the possible mechanism was explored. The results showed that TBP at concentrations ≥0.2 mg L^-1 significantly inhibited P. tricornutum growth in a clear dose-response manner, with 72-h EC₁₀, EC₂₀, EC₅₀ and EC₉₀ values of 0.067, 0.101, 0.219 and 0.716 mg L^-1, respectively. Algal cells treated with TBP exhibited distorted shapes, ruptured cell membranes and damaged organelles, especially mitochondria. Additionally, apoptosis was triggered, followed by a decrease in mitochondrial membrane potential, indicating that cellular damage occurred during exposure. Although the activities of two antioxidant enzymes, superoxide peroxidase and catalase, were upregulated by TBP at 1.2 mg L^-1, excess reactive oxygen species (ROS) and malondialdehyde still accumulated in algal cells after exposure, suggesting that the cells experienced oxidative stress. Moreover, both growth inhibition and apoptosis were positively correlated with ROS levels and were ameliorated by pretreatment with the ROS scavenger N-acetyl-l-cysteine. Taken together, the results indicate that TBP exposure leads to growth inhibition and cellular damage in P. tricornutum, and a ROS-mediated pathway might contribute to these observed toxicological effects.