Oxidative stress response in microalgae and bivalves induced by different environmental conditions

IARA ROCCHETTA

Delmenshorst

Conferencia; International Conference: Environmental induced oxidative stress in nature and experiment; 2012

Hanse-Wissenschaftskolleg. Institute for Advanced Study

The objective of this work was to evaluate the effects of aquatic pollutions (heavy metals and wasted discharges) in different freshwater organisms for future bioremediation purposes. For that, we studied: growth curves, morphological changes, carbohydrate, protein and lipid composition (pigments in algae) and gene expression associated with the stress condition.The organisms that we have used have been: Microalgae: two strains of Euglena gracilis (Protist, Euglenoid group)were compared: MAT (isolated from a highly polluted river of Buenos Aires, Matanza   River) and UTEX 753 (comercial). Bivalves: Diplodon chilensis (Bivalvia, Hyriidae), a native patagonian freshwater bivalve. Bioassays (EPA protocols (IC50)) were conducted in different culture conditions finding that MAT strain showed to be a tolerant strain (Cr(VI), Cu, Sn, Cd, HCB). We found that in response to a heavy metals, mainly chromium: 1) defense/detoxification system was the same MAT-UTEX, major differences were observed in the  GSH + SOD activity being higher in MAT strain, 2) SOD activity was mainly a response of MAT strain and was not in relation to chromium response and 3) MAT (strain isolated from polluted river) showed higher stress response in relation to the gene expression and metabolic parameters presenting a more efficient defense system under stress condition. Field studies were conducted with the bivalves. Population (abundance, frequency, growth curves, ageing data) and morphometrics parameters, condition index, morphological changes and antioxidant defense and oxidative damage (GSH/GSSG, GST, SOD, MDA, carbonyls) were analyzed. Two populations were compared, one come from an urban polluted place (mainly fecal bacteria high amount) and the other from a control place from Lacar lake (Yuco), Neuquen province, Argentina. We found that the mean size was higher for SMA organisms in compare to the controls (71 mm vs. 37 mm  length) in relation to the higher growth rate found for the SMA population. On the other hand, the density was lower in SMA bivalves (33 ± 8 indiv./m2  vs. 176±90 indiv./m2). The sewage discharge of SMA city affected: 1)population parameters, as density (<indiv./m2), mean size distribution (> size), higher growth rate and condition index (DGL/SL), 2) stress parameters (GSH, GST, MDA) suggesting a higher metabolism of these organisms, 3)adaptive response to chronic wastewater exposure with oxidative stress not fully compensated (high levels of TBARS, a lipid peroxidation index), 4) This oxidative status was well tolerated by adults as no juvenile recruitment was observed (< 7y) and 5) D. chilensis adult can filter and digest fecal bacteria at high concentrations, making this species a promising tool for bioremediation of urban pollution. Using two different models as microalgae and bivalves we can conclude that the environmental factors can affect the oxidative state resulting in an adaptive response.