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

Information regarding the effect of nanoscale titanium dioxide particles (nTiO) on the environment under dark conditions is scarce, and the effect of nTiO 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 nTiO 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 nTiO (5-18 mg/mL). At long exposure times (~3 days), relatively low doses of nTiO (≤9 mg/mL) stimulated the growth of macroplasmodium and oxidative stress without DNA damage, whereas higher doses of nTiO (≥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 nTiO 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 nTiO could induce oxidative stress or damage in P. polycephalum even under dark conditions and suggesting that the release of nTiO could lead to a growth imbalance of slime molds in the environment.