Early genotoxic effects in gill cells and haemocytes of Dreissena polymorpha exposed to cadmium, B[a]P and a combination of B[a]P and Cd

Monitoring of DNA damage in haemocytes of freshwater mussel Sinanodonta woodiana sampled from the Velika Morava River in Serbia with the comet assay

This study was undertaken to investigate the potential of the freshwater mussel Sinanodonta woodiana for detection of genotoxic pollution of the environment. Study was performed at two sites in the Velika Morava River, from May 2010 to February 2011. The alkaline comet assay on haemocytes was used, and the olive tail moment (OTM) was chosen as a measure of DNA damage. The specimens held on acclimation under controlled laboratory conditions for 10d were used as a control. Chemical analysis revealed the presence of phosphates and increased concentrations of zinc, copper and nickel at both sites during the entire sampling period. The values of OTM in mussels collected from the environment, significantly correlated with the concentration of zinc (r=0.6248), temperature (r=0.7006) and dissolved oxygen (r=0.7738). Seasonal variations in genotoxic response were observed, with the highest OTM values obtained during summer months. Preliminary results of the in vitro study indicated the effect of water temperature on genotoxic response to zinc and cadmium in S. woodiana suggesting that the presence of genotoxic pollutants during months with lower temperature could be under-estimated. Obtained results indicate that S. woodiana could be a valuable tool for active biomonitoring of aquatic environments and emphasizes the importance of seasonal genotoxic monitoring with this organism.

Seasonal and PAH impact on DNA strand-break levels in gills of transplanted zebra mussels

Genotoxicity endpoints are useful tools to biomonitor the physicochemical and biological quality of aquatic ecosystems. A caging study on the freshwater bivalve Dreissena polymorpha was planned to run over four seasons in the Seine River basin in order to assess whether DNA damage measured in transplanted mussels to polluted area vary according to seasonal changes. Three sites were chosen along the Seine River, one upstream from Paris and two downstream, corresponding to a chemical gradient of water contamination. The DNA strand break (comet assay) and chromosomal damage (micronucleus test) were measured in caged mussels at each site and in winter, spring and summer, along with PAH water contamination, PAH bioaccumulation, the mussel condition index (CI), the gonado-somatic index (GSI) and the filtration rate (FR). The level of DNA strand break measured in winter was low and increased in spring, concomitantly with FR and GSI. Over the same period, micronucleus (MN) frequency and PAH bioaccumulation decreased significantly in caged mussels, with both parameters positively correlated to each other. DNA strand-break levels and MN frequencies showed inter-site variations corresponding to the chemical contamination gradient. These two genotoxicity endpoints usefully complement each other in field studies. These results show that the MN test and comet assay, when applied to gill cells of caged zebra mussels, are sensitive tools for freshwater genotoxicity monitoring.

Protozoa interaction with aquatic invertebrate: interest for watercourses biomonitoring

Toxoplasma gondii, Cryptosporidium parvum, and Giardia duodenalis are human waterborne protozoa. These worldwide parasites had been detected in various watercourses as recreational, surface, drinking, river, and seawater. As of today, water protozoa detection was based on large water filtration and on sample concentration. Another tool like aquatic invertebrate parasitism could be used for sanitary and environmental biomonitoring. In fact, organisms like filter feeders could already filtrate and concentrate protozoa directly in their tissues in proportion to ambient concentration. So molluscan shellfish can be used as a bioindicator of protozoa contamination level in a site since they were sedentary. Nevertheless, only a few researches had focused on nonspecific parasitism like protozoa infection on aquatic invertebrates. Objectives of this review are twofold: Firstly, an overview of protozoa in worldwide water was presented. Secondly, current knowledge of protozoa parasitism on aquatic invertebrates was detailed and the lack of data of their biological impact was pointed out.

DNA strand breaks detected in embryos of the adult snails, Potamopyrgus antipodarum, and in neonates exposed to genotoxic chemicals

We tested the freshwater mudsnail Potamopyrgus antipodarum, which is a species that has already been used for endocrine-disrupting compounds (EDCs) to determine whether early life stages of aquatic organisms are sensitive to genotoxic chemicals. For this purpose, we first developed the alkaline comet assay on adults, embryos, and neonates. The comet assay protocol was validated on both embryonic cells exposed in vitro to hydrogen peroxide and adult snails in the reproducing stage exposed to methyl methane sulfonate. During the latter experiment, DNA strand breaks were investigated on both embryonic cells and on adult gill cells. The second part of this study investigated the stability of DNA strand breaks in adult reproducing snails and neonates exposed to cadmium (Cd) and bisphenol A for 8 days. Hydrogen peroxide-induced DNA strand breaks in vitro in isolated embryonic cells. Exposure of adult reproducing snails to methyl methane sulfonate for 24h induced DNA strand breaks in embryos. Bisphenol A induced a significant increase in the DNA strand-break level in whole embryonic cells and whole neonate cells. Cd was genotoxic for both embryos and neonates during the exposure time and also after 7 days of depuration, suggesting that Cd could inhibit DNA repair enzymes. These preliminary results on this original model have encouraged us to consider the impact of genotoxic environmental contaminants on the F1 generation.

Detection of 8-oxodG in Dreissena polymorpha gill cells exposed to model contaminants

Genotoxic end-points are routinely measured in various sentinel organisms in aquatic environments in order to monitor the impact of water pollution on organisms. As a first step towards the evaluation of oxidative DNA damage (8-oxodG) in organisms exposed to chemical water pollution, we have optimized the association between the comet assay and the hOGG1 enzyme for use on zebra mussel (Dreissena polymorpha) gill cells by in vitro exposure to H₂O₂. Firstly, we observed that in vitro exposure of D. polymorpha gill cells to benzo[a]pyrene (B[a]P, 98.4nM) induced an increase of the Olive Tail Moment (OTM) in both the comet-hOGG1 and comet-Fpg assays, indicating that B[a]P causes oxidative DNA damage. By contrast, methylmethane sulfonate (MMS, 33μM) only induced an increase of the Fpg-sensitive sites, indicating that MMS caused alkylating DNA damage and confirming that hOGG1 does not detect alkylating damage. Thus, the hOGG1 enzyme seems to be more specific towards oxidative DNA damage, such as 8-oxodG than Fpg. Secondly, as was observed in vitro, the in vivo exposure of D. polymorpha to B[a]P (24.6 and 98.4nM) increased oxidative DNA damage in gill cells, whereas only Fpg-sensitive sites were detected in mussels exposed to MMS (240μM). These results show that the comet-hOGG1 assay detects oxidative DNA lesions induced in vitro by H₂O₂ and in vivo with BaP. The comet-hOGG1 assay will be used to detect oxidative DNA lesions (8-oxodG) in mussels exposed in situ.

Differentially displayed genes with oxygen depletion stress and transcriptional responses in the marine mussel, Mytilus galloprovincialis

Hypoxic events affecting aquatic environments have been reported worldwide and the hypoxia caused by eutrophication is considered one of the serious threats to coastal marine ecosystems. To investigate the molecular-level responses of marine organisms exposed to oxygen depletion stress and to explore the differentially expressed genes induced or repressed by hypoxia, differential display polymerase chain reaction (DD-PCR) was used with mRNAs from the marine mussel, Mytilus galloprovincialis, under oxygen depletion and normal oxygen conditions. In total, 107 cDNA clones were differentially expressed under hypoxic conditions relative to the control mussel group. The differentially expressed genes were analyzed to determine the effects of hypoxia. They were classified into five functional categories: information storage and processing, cellular processes and signaling, metabolism, predicted general function only, and function unknown. The differentially expressed genes were predominantly associated with cellular processing and signaling, and they were particularly related to the signal transduction mechanism, posttranslational modification, and chaperone functions. The observed differences in the DD-PCR of 10 genes (encoding elongation factor 1 alpha, heat shock protein 90, calcium/calmodulin-dependent protein kinase II, GTPase-activating protein, 18S ribosomal RNA, cytochrome oxidase subunit 1, ATP synthase, chitinase, phosphoglycerate/bisphosphoglycerate mutase family protein, and the nicotinic acetylcholine receptor) were confirmed by quantitative RT-PCR and their transcriptional changes in the mussels exposed to hypoxic conditions for 24-72 h were investigated. These results identify biomarker genes for hypoxic stress and provide molecular-level information about the effects of oxygen depletion on marine bivalves.