Abstract
The effect of chronic exposure to Escherichia coli on morphometrical parameters, different antioxidant defenses, lipid peroxidation and protein oxidation has been studied in digestive gland of the freshwater mussel Diplodon chilensis in the laboratory during 6 weeks. In, a parallel field study, we evaluated morphometrical and oxidative stress parameters in digestive glands of mussels collected from a sewage polluted area (SMA) and from a pristine area (control). Both sites were characterized by analyzing bacteriological and physic-chemical parameters. In the laboratory D. chilensis was able to filter bacteria at high concentrations with a clearing rate of 0.510 ± 0.036 L/h per gram of dry soft tissue mass. The digestive gland mass to shell length ratio (DGM/SL), reduced glutathione (GSH), lipid peroxidation, as concentration of thiobartituric acid reactive substances (TBARS), and glutathione-S-transferase (GST) activity of mussels fed with bacteria were significantly higher than those of control mussels after the fourth week. Fecal bacteria in lake water samples were undetectable in the control, and higher than 24,000 MPN (most probable number)/100 mL in SMA. DGM/SL was higher in SMA. No differences between sites were observed in total lipid and protein content, neither in superoxide dismutase activity. GSH content was higher in SMA, with no difference in the oxidized form. GST activity and MDA were significantly higher in SMA but protein oxidation was not affected.
Highlights
Bivalve mollusks are capable of removing large amounts of phytoplankton and other suspended particulate matter, helping to clear the water column (Nakamura and Kerciku 2000; Yamamuro et al 2000)
GSH level started to increase at day 14 in treated individuals and became significantly higher than the control at day 42 (ANOVA P < 0.01) (Fig. 1) while GST activity and lipid peroxidation increased since day 35 and 42, respectively, in mussels fed with bacteria (ANOVA P < 0.001 and P < 0.05, respectively) (Figs. 2 and 3)
GST activity was increased in treated mussels by 68% (0.848 ± 0.034 vs. 0.505 ± 0.106 U/mg protein) while lipid peroxidation was increased by 37% (2.42 ± 0.27 vs. 1.77 ± 0.23 mol thiobartituric acid reactive substances (TBARS)/mg protein)
Summary
Bivalve mollusks are capable of removing large amounts of phytoplankton and other suspended particulate matter, helping to clear the water column (Nakamura and Kerciku 2000; Yamamuro et al 2000) For this reason, these filter-feeding animals have become useful biological tools for mitigating the eutrophication and pollution of coastal ecosystems (Nelson et al 2004; Gifford et al 2005; Lindahl et al 2005). The freshwater mussel Diplodon chilensis (Hyriidae) is abundant in lakes and rivers of west Patagonia, Argentina and is widely distributed in temperate and cold lakes of Chile (Bonetto 1973; Valdovinos and Pedreros 2007) This species has been considered as a potential bioremediation tool, since it is able to reduce chlorophyll a and nutrient levels in co-cultures with salmon (Soto and Mena 1999) as well as to clearing coliform bacteria from domiciliary wells (Lara et al 2002). These authors have demonstrated the ability of this species to reduce the impact of fish farming on several water quality parameters such as total suspended solids, total phosphorous, nitrite and chemical oxygen demand
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