Interactive effects of cadmium and hypoxia on metabolic responses and bacterial loads of eastern oysters Crassostrea virginica Gmelin |
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Authors: | Ivanina Anna V Froelich Brett Williams Tiffany Sokolov Eugene P Oliver James D Sokolova Inna M |
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Institution: | a Biology Department, University of North Carolina at Charlotte, 9201 University City Blvd., Charlotte, NC 28223, United States b Department of General Surgery, Carolinas Medical Center, 1000 Blythe Blvd., Charlotte, NC 28203-5871, United States |
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Abstract: | Pollution by toxic metals including cadmium (Cd) and hypoxia are important stressors in estuaries and coastal waters which may interactively affect sessile benthic organisms, such as oysters. We studied metabolic responses to prolonged hypoxic acclimation (2 weeks at 5% O2) in control and Cd-exposed (30 d at 50 μg L−1 Cd) oysters Crassostrea virginica, and analyzed the effects of these stressors on abundance of Vibrio spp. in oysters. Hypoxia-acclimated oysters retained normal standard metabolic rates (SMR) at 5% O2, in contrast to a decline of SMR observed during acute hypoxia. However, oysters spent more time actively ventilating in hypoxia than normoxia resulting in enhanced Cd uptake and 2.7-fold higher tissue Cd burdens in hypoxia. Cd exposure led to a significant decrease in tissue glycogen stores, increase in free glucose levels and elevated activity of glycolytic enzymes (hexokinase and aldolase) indicating a greater dependence on carbohydrate catabolism. A compensatory increase in activities of two key mitochondrial enzymes (citrate synthase and cytochrome c oxidase) was found during prolonged hypoxia in control oysters but suppressed in Cd-exposed ones. Cd exposure also resulted in a significant increase in abundance of Vibrio parahaemolyticus and Vibrio vulnificus levels during normoxia and hypoxia, respectively. Overall, Cd- and hypoxia-induced changes in metabolic profile, Cd accumulation and bacterial flora of oysters indicate that these stressors can synergistically impact energy homeostasis, performance and survival of oysters in polluted estuaries and have significant consequences for transfer of Cd and bacterial pathogens to the higher levels of the food chain. |
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Keywords: | AEC adenylate energy charge ADP adenosine-5&prime -diphosphate AMP adenosine-5&prime -monophosphate ATP adenosine-5&prime -triphosphate ASW artificial seawater Cd cadmium cDNA complementary DNA COX complex IV (cytochrome c oxidase) CS citrate synthase E amplification efficiency EDTA ethylenediaminetetraacetic acid HK hexokinase HIF-1 hypoxia-inducible factor-1 mRNA messenger RNA NADH nicotinamide adenine dinucleotide NADPH nicotinamide adenine dinucleotide phosphate PCA perchloric acid PCR polymerase chain reaction PEP phosphoenolpyruvate PHD2 prolyl hydroxylase 2 PcO2 critical oxygen tension SMR standard metabolic rate qRT-PCR quantitative real-time PCR |
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