The effect of post-biotics-enriched diet on the antioxidant capacity in Mytilus galloprovincialis exposed to CuO.

This study explores the effects of copper (I) oxide (Cu₂O) nanoparticle exposure on Mytilus galloprovincialis gills and the modulation of oxidative stress by a diet enriched with a postbiotic derived from kefir microorganisms. Postbiotics, which include components such as proteins, lipopolysaccharides, and short-chain fatty acids, have shown biological benefits, including enhancing gut health and modulating immunity. They are known for their antioxidant properties, which can counteract oxidative stress by scavenging free radicals, making them useful in both human and animal health. Mussels were exposed to 2 mg L of Cu₂O nanoparticles for three days. Nanoparticle characterization showed rapid agglomeration in seawater, with hydrodynamic diameters increasing from 76 ± 11 nm to 529 ± 75 nm within 24-48 h. Biochemical analyses revealed a significant increase in catalase (CAT) activity in mussels exposed to Cu₂O nanoparticles (G1⁺ group; p < 0.0001), which was not observed in mussels exposed to Cu₂O nanoparticles after feeding with postbiotics (G2⁺ group); indicating the postbiotic's protective role. Glutathione reductase (GR) activity was significantly reduced in the G1⁺ group (p < 0.01), but maintained at control levels in the G2⁺ group. While glutathione S-transferase (GST) activity decreased in both exposed groups, the reduction was notably less pronounced in the G2⁺ group compared to G1⁺, suggesting mitigation of the pollutant's adverse effects on the GST-mediated detoxification pathway. A strong negative correlation was observed between CAT and GST (and to a lesser extent GR), indicating that Cu₂O exposure at the tested concentrations can overburden glutathione defense pathways despite robust CAT activity. These results highlight the potential of postbiotics from kefir microorganisms as effective feed additives in mussel aquaculture to enhance resilience against environmental pollutants and mitigate oxidative stress.