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.
Keywords: Dark conditions; Nanoscale TiO2; Oxidative stress; Physarum polycephalum; Toxicity.