Biomarkers response to zinc exposure in the symbiont-bearing foraminifer Amphistegina lessonii (Amphisteginidae, Foraminifera)

The acute effects of zinc (Zn) were evaluated in the symbiont-bearing foraminifer Amphistegina lessonii from the Fernando de Noronha Archipelago (Northeastern Brazil). Foraminifers were acutely (48h) exposed to dissolved Zn concentrations ranging from 9.5 to 93.4μg Zn/l. Endpoints analyzed included mortality, visual alterations (white spots and dark-brown areas in the test), oxidative stress biomarkers (reactive oxygen species generation, lipid peroxidation and total superoxide dismutase activity), and concentration of metallothionein-like proteins in whole individuals after Zn exposure. No significant mortality was observed during the 48-h exposure period to waterborne Zn. However, a significant percentage of individuals showed visual alterations (white spots and/or dark-brown areas in the test) after 24 and 48h of Zn exposure. In fact, a significant positive correlation between this endpoint and dissolved Zn concentrations was observed for both times of exposure. Based on this endpoint, the 24-h and 48-h EC50 values and their corresponding 95% confidence intervals for total measured Zn concentrations were calculated as 112.2 (86.5–199.5) and 43.6 (34.9–57.3) μg Zn/l, respectively. Based on the dissolved Zn concentrations, they were 100.7 (75.3–175.9) and 38.2 (29.7–49.4) μg Zn/l, respectively. Therefore, a significant increase in Zn toxicity was observed with increasing time of exposure. After 48h of Zn exposure, whole body antioxidant capacity was lower in normal-appearing individuals than in those at the initial stage of bleaching. Increases in lipid peroxidation, metallothionein-like protein concentration and total SOD activity was observed at a greater extent in pale/partly-bleached individuals associated with an increased Zn toxicity measured as visual alterations. These findings suggest that an activation of some components of the antioxidant system occurred in A. lessonii to counteract the oxidative stress induced by Zn exposure, and consequently avoid a possible complete loss of the symbiont.