Effect of oxidative stress from nanoscale TiO₂ particles on a Physarum polycephalum macroplasmodium under dark...

Information regarding the effect of nanoscale titanium dioxide particles (nTiO₂) on the environment under dark conditions is scarce, and the effect of nTiO₂ on fungi is largely unknown. Due to its huge size and high sensitivity to external stimuli, the slime mold fungi cell, Physarum polycephalum macroplasmodium, was utilized as a novel subject for the toxicity investigations in the present study, and oxidative stress from nTiO₂ on the macroplasmodium was assessed under dark conditions. Short exposure (2-3 h) caused an intracellular reactive oxygen species (ROS) imbalance, and an anti-oxidative mechanism was activated from intermediate doses of nTiO₂ (5-18 mg/mL). At long exposure times (~3 days), relatively low doses of nTiO₂ (≤9 mg/mL) stimulated the growth of macroplasmodium and oxidative stress without DNA damage, whereas higher doses of nTiO₂ (≥15 mg/mL) led to growth inhibition, significant DNA oxidative damage, and activation of the DNA single-strand repairing system. Although DNA oxidative damage was decreased to the same level as the control group by the supplementation of the anti-oxidant vitamin C, growth of the macroplasmodium failed to be completely restored. We inferred that nTiO₂ induced a complicated toxicity effect on P. polycephalum in addition to DNA oxidative damage. Taken as a whole, the present study implied the probability of using P. polycephalum macroplasmodium for toxicity studies at the single-cell level, indicating that nTiO₂ could induce oxidative stress or damage in P. polycephalum even under dark conditions and suggesting that the release of nTiO₂ could lead to a growth imbalance of slime molds in the environment.