Gene expression responses unveil the negative effects of Olive Mill Wastewater on Gammarus komareki (Amphipoda: Gammaridae)

Olive Mill Wastewater (OMW) is a major organic pollutant, particularly in Mediterranean countries with intensive olive oil production. In this study, the toxic effects of OMW were tested on a freshwater macroinvertebrate, Gammarus komareki. Animals were exposed to different concentrations of 1/5, 1/10, and 1/20 of the previously calculated 72-h LC50 (LC50 = 3.65%) and was applied as high (0.73%), medium (0.365%) and low (0.1825%) levels, respectively for 20 days. At exposure, female and male individuals from each group were sampled separately. Samples were analyzed for the expression levels of antioxidant defences (cat, gst, se-gpx, and mn-sod), reproduction (vitellogenin-like protein, vtg), respiration (hemocyanin, hc), antitoxic defences (heat shock protein 70, hsp70), and molting (molt-inhibiting hormone, mih) related genes. Results revealed that the expression levels of vtg gene in females exposed to low doses were increased significantly compared to other groups; however, its levels were decreased in group exposed to high doses compared to the control and other groups. The mRNA expression levels of mn-sod and se-gpx genes of males and female individuals exposed to low OMW doses increased significantly compared to other doses. The mRNA expression levels of gst gene increased in males and females exposed to moderate doses and only in males exposed to low doses compared to other groups. The mRNA expression levels of cat gene of females were similar in all groups, while their levels were higher in males exposed to OMW than in the control group. The expression values of hsp70 gene were significantly decreased in females and all males exposed to high doses of OMW. On the other hand, the mih gene expression in females was increased at low doses of OMW, while decreased in the groups exposed to high doses compared to the control group. In male individuals, the mih expression levels significantly increased in all experimental groups. The expression of the hc gene was decreased in male and female individuals exposed to all doses of OMW compared to the control group. To put it briefly, the great variations in the gene expression levels in groups exposed to OMW underlines the toxic effects of this effluent and its negative impacts on the aquatic organisms.