Autophagy: A newly discovered protective mechanism in the marine rotifer Brachionus plicatilis in response to BDE-47 exposure

Response of life-history traits, population dynamics, offspring size of Brachionus plicatilis exposure to BTBPE

The novel brominated flame retardant 1, 2-bis (2,4,6 tribromophenoxy) ethane (BTBPE) has been widely used since the mid-1970s and detected in the aquatic environment and organisms; however, little information is available regarding its biotoxicity. In this study, the life-history parameters, transcriptomic regulation, multi-generational offspring size, and population dynamics of rotifers were determined in response to BTBPE (0, 0.01, 1, and 100 μg/L). The results showed that BTBPE (>1 μg/L) significantly increased the pre-reproductive time, shortened both reproduction periods and the lifespan, and decreased the total number of rotifer offspring. Transcriptomic analysis revealed that the expression of key genes involved in the pathways of citrate cycle, 2-oxocarboxylic acid metabolism, carbon metabolism, and propanoate metabolism was affected. Moreover, BTBPE has transgenerational effects on rotifers, the size of the F1 to F5 generations decreased significantly in response to BTBPE. Finally, the population density in the 100 μg/L BTBPE treatment group was significantly reduced by 30 % compared to the control group, suggesting that the population growth of rotifers was inhibited by BTBPE exposure. The findings of this study indicate that BTBPE has effects on the individual reproduction, population growth, offspring quality, and energy metabolism of rotifers. These findings highlighted the potential impacts of BTBPE on dominant zooplankton species, providing useful baseline information for evaluating the potential ecological risk of novel brominated flame retardant.

Transcriptome analysis reveals the different toxic mechanism of three HBCD diastereoisomers to Brachionus plicatilis based on chemical defensome

The emerging contaminants hexabromocyclododecanes (HBCDs) are proved to exhibit highly reproductive toxicity to marine rotifer Brachionus plicatilis, but how about the toxic differentiation among three diastereoisomers of HBCD, and what's the possible hidden mechanism? B. plicatilis was exposed to different concentrations of HBCD diastereoisomers, and the results showed that α-, β- and γ-HBCD exhibited various toxicity on it, the adverse effects on individual life history traits included shortened lifespan, shortened body length and reduced offspring number. Population dynamics analysis showed that the maximum population density and time to reach it were also significantly influenced. The integrated biomarker responses (IBR) were constructed based on key life history traits and population dynamics indicators, and the comprehensive toxicity ranking of HBCD diastereoisomers was β-HBCD> α-HBCD> γ-HBCD, which was consistent with acute experimental results. Results of transcriptome with emphasis on chemical defensome was conducted. Genes including cytochrome P450 enzymes (CYP450s), aldehyde dehydrogenases (ALDHs), glutathione S-transferases (GSTs) and SOD were upregulated under γ-HBCD compared to those under α- and β-HBCD. Results of molecular docking suggested γ-HBCD had stronger affinity with aryl hydrocarbon receptor (AhR) that made it more easily activate the subsequent components of the defending pathway. Moreover, transcriptome result showed the level of autophagy, the newly found protective pathway in B. plicatilis was higher under α- and β-HBCD than that under γ-HBCD and the TEM observation result provided the consist directly proof. The chemical defensome and the subsequently autophagy seemed to be the hidden mechanism for the toxicity differentiation of the HBCD diastereoisomers.

Ecological risk assessment for BDE-47 in marine environment based on species sensitivity distribution method

BDE-47 is the most abundant and toxic congener in the marine environment. Assessing the ecological risk of BDE-47 in seawater is of great importance to protect the marine species. However, the ecological risks of BDE-47 on marine species is still limited. In the present study, the hazardous concentrations for 5 % of species (HC5) values of BDE-47 were derived by species sensitivity distributions (SSD), the short-term water quality criteria (SWQC) and long-term water quality criteria (LWQC) were acquired from HC5. Moreover, the marine ecological risk of BDE-47 was assessed by the risk quotient (RQ) method in the coastal area of China. The SWQC and LWQC were 1.06 μg/L and 0.61 μg/L, respectively. According to published literature, the concentrations of BDE-47 ranged from undetected to 9.06 ng/L, BDE-47 has no risk to marine species in most coastal areas, but might show low risk for a long exposure time in the coastal mariculture area of China. This study provides a new approach for the derivation of the WQC and the ecological risk assessment of BDE-47, which is essential for the protection of marine species and provides guidance to manage the concentration of BDE-47 for administrative department.

Hexabromocyclododecane-induced reproductive toxicity in Brachionus plicatilis: Impacts and assessment

Hexabromocyclododecane (HBCD), third-generation brominated flame retardants (BRFs), has aroused worldwide concern because of its wide application and potentially negative impacts on marine ecosystems, but an information gap still exists regarding marine low-trophic organisms. Brachionus plicatilis, the model marine zooplankton, was used in the present study, and its reproductive responses were used as the endpoint to indicate HBCD-induced toxicity. HBCD was suggested to be extremely highly toxic compounds regarding the 96 h-LC50 of 0.58 mg L-1. The sublethal exposure of HBCD injured the reproduction of B. plicatilis: The total number of offspring per female and the key population index calculated from the life table, including the intrinsic rate of population increase (rm) and net reproductive rate (R0), were significantly influenced in a concentration-dependent manner. The reproductive process was also altered, as indicated by the first spawning time, first hatching time and oocyst development time. At the same time, individual survival and growth (body length) were also negatively affected by HBCD. Reactive oxygen species (ROS) were suggested to be responsible for reproductive toxicity mainly because the total ROS contents as well as the main components of •OH and H2O2 greatly increased and resulted in the oxidative imbalance that presented as malondialdehyde (MDA) elevation. Simultaneous activation of the glutathione antioxidant system was accompanied by the apoptosis marker enzymes Caspase-3 and 9, as well as the correlation between ROS content, physiological alteration and cell apoptosis, providing further evidence for this. The integrated biomarker response (IBR) and adverse outcome pathway (AOP) showed that HBCD had a significant toxic effect on B. plicatilis near the concentration range of 96 h-LC50. The establishment of this concentration range will provide a reliable reference for future environmental concentration warning of HBCD in marine.

Molecular characterization and expression analysis of a QM protein gene in Chinese mitten crab Eriocheir sinensis

QM protein was previously discovered as a tumor suppressor, and numerous studies have shown that QM protein also played important roles in the immune responses. To investigate the potential roles of the QM protein gene in Eriocheir sinensis, the QM protein gene (designated as EsQM) has been cloned from E. sinensis using the rapid amplification of cDNA ends (RACE) technique. The cDNA of EsQM is 781 bp in length, consisting of a 654 bp open reading frame (ORF), encoding 219 amino acids, a 27 bp 5' untranslated region (UTR) and a 94 bp 3' UTR. The EsQM protein has a calculated molecular weight of 25.4 kDa and a theoretical isoelectric point of 10.10. The deduced protein sequence of EsQM contains a Ribosomal_L16 domain, an SH3-binding motif, an N-acylation site, two putative antibiotic binding sites, two putative protein kinase C phosphorylation sites, and two amidation sites. EsQM is extremely conserved and exhibits more than 85% similarities to previously identified arthropod QM protein genes. By real-time quantitative PCR (qPCR) analysis, we found that EsQM mRNA transcripts were detectable in all the examined tissues, with the highest expression in hemocytes. The mRNA expression of EsQM in hemocytes was significantly upregulated after the stimulation of Aeromonas hydrophila or polybrominated diphenyl ether-47 (BDE-47). Moreover, EsQM mRNA expression in hemocytes responded more quickly and lasted longer when stimulated by A.hydrophila than BDE-47. Thus, EsQM can respond to bacterial infection and environmental pollution, and might be involved in the defense mechanism to both biological and non-biological stimulation of arthropods.

Purine Metabolism and Pyrimidine Metabolism Alteration Is a Potential Mechanism of BDE-47-Induced Apoptosis in Marine Rotifer Brachionus plicatilis

This present study was conducted to provide evidence and an explanation for the apoptosis that occurs in the marine rotifer Brachionus plicatilis when facing 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) stress. Metabolomics analysis showed that aminoacyl-tRNA biosynthesis, valine, leucine and isoleucine biosynthesis, and arginine biosynthesis were the top three sensitive pathways to BDE-47 exposure, which resulted in the reduction in the amino acid pool level. Pyrimidine metabolism and purine metabolism pathways were also significantly influenced, and the purine and pyrimidine content were obviously reduced in the low (0.02 mg/L) and middle (0.1 mg/L) concentration groups while increased in the high (0.5 mg/L) concentration group, evidencing the disorder of nucleotide synthesis and decomposition in B. plicatilis. The biochemical detection of the key enzymes in purine metabolism and pyrimidine metabolism showed the downregulation of Glutamine Synthetase (GS) protein expression and the elevation of Xanthine Oxidase (XOD) activity, which suggested the impaired DNA repair and ROS overproduction. The content of DNA damage biomarker (8-OHdG) increased in treatment groups, and the p53 signaling pathway was found to be activated, as indicated by the elevation of the p53 protein expression and Bax/Bcl-2 ratio. The ROS scavenger (N-acetyl-L-cysteine, NAC) addition effectively alleviated not only ROS overproduction but also DNA damage as well as the activation of apoptosis. The combined results backed up the speculation that purine metabolism and pyrimidine metabolism alteration play a pivotal role in BDE-47-induced ROS overproduction and DNA damage, and the consequent activation of the p53 signaling pathway led to the observed apoptosis in B. plicatilis.