Study On Toxicity And Related Mechanisms Of Nano-titanium Dioxide To Pichia Pastoris

Titanium dioxide?TiO₂? nanomaterials are currently arousing great interest thanks to their unique properties. TiO₂ nanoparticles?NPs? are implemented in a wide range of applications, such as production of paints, paper, cosmetics, medical equipment, etc. And these NPs have been one of the earliest industrially produced and the most highly manufactured nanomaterials. The widespread production and use of nano-TiO₂ inevitably give rise to heavily releasing of these nanoparticles into the environments, resulting in an enhanced exposure of environmental producers, consumers and decomposers to TiO₂ NPs. Therefore, it is necessary and reasonable to understand their adverse effects on environment and organisms. However, most studies focus on cells and tissues of animals and plants, and the potential hazardous effects of TiO₂ NPs on fungi are still insufficient and related mechanisms need further elucidation. As the principal decomposers in ecosystem, fungi are abundant around the world and play an essential role in maintaining ecological cycles and balances. Thus evaluating possible toxicity of TiO₂ NPs on fungi makes much sense in ecological protection. The methylotrophic yeast Pichia pastoris, proved to be an excellent system for high-level expression of heterologous proteins, is also a good eukaryotic model organism for studies on the metabolism of fatty acid biosynthesis. In this study, we investigated the potential effect of anatase TiO₂ NPs on Pichia pastoris GS115, and discussed their possible toxic mechanisms. The main results are demonstrated as follows.?1? We found the anatase TiO₂ nanoparticles had low toxicity to the oil-producing model organism, P. pastoris, and this toxicity contributes to cell membrane damage, enhanced vacuolar membrane permeabilization?VMP? and cell wall damage-related reactive oxygen species?ROS? accumulation. More importantly, the synthesized TiO₂ NPs had a positive effect on production of unsaturated fatty acids?UFAs?, which is associated with enhancement of lipid droplet?LD? formation and up-regulation of UFA synthesis-related genes. The study emphasizes the positive effect of TiO₂ nanoparticles on production of UFAs which plays a role in alleviating the cytotoxicity of the nanomaterials to Pichia pastoris. The findings contribute to further studies on toxic mechanisms of these nanomaterials and resultant defending pathways of eukaryotic cells.?2? Results showed that TiO₂ NPs could enter cells and cause mitochondrial disturbance and fragmentation, which contributes to the cytotoxicity. Their toxicity was not attributed to apoptosis or autophagy, but damage to the ROS-scavenging system, especially metabolic balance of GSH. It led cellar ROS could not be scavenged effectively, thus inducing death of cells.?3? TiO₂ nanoparticles with different crystal forms have different toxic mechanism in cells. This study found that the toxicity of anatase TiO₂ to P. pastoris was stronger than rutile TiO₂. With a stronger capacity to interact with cells, anatase TiO₂ showed endocytosis-dependent toxicity and could impair ROS scavenging system, thus affecting regular functions of the treated cells. Rutile TiO₂ could stimulate activation of cell apoptosis pathway, leading to nuclear DNA fragmentation and cell death.