Gravitational Effect of Zinc Oxide Nanoparticle Microbicidal Activity
Microgravity has been shown to change gene expression patterns, changes in cell morphology, and changes in cellular proliferation, among various cell types and organisms. We seek to determine whether the microbicidal activities of Zinc Oxide nanoparticles (ZnO NPs) are retained in modeled microgravity conditions. ZnO NPs induce cell death by promoting the formation of Reactive Oxygen Species (ROS) and overwhelming the cell with oxidative stress. We are particularly concerned that the antimicrobial activity of ZnO NPs will be rendered ineffective during spaceflight. This study seeks to elucidate the mechanisms which control changes in ZnO NPs cytotoxicity in modeled microgravity conditions (MMG) versus normal gravity (NG) conditions. For this study, Low-Shear Modeled Microgravity conditions were obtained using a rotating wall vessel bioreactor (RWV), designed by the National Aeronautics and Space Administration. The RWV works by rotating a cylinder that randomizes the gravity vectors on the cells so there is a low shear environment for the cells to grow in, and this simulates the effects of weightlessness. By shifting the position of the RWV, we can control whether the cells grow in NG or MMG. The ZnO NPs used in this experiment were synthesized a sol-gel approach and characterized using X-ray Diffraction. Saccharomyces cerevisiae was used as the model microbe in this study. This simple eukaryote is inexpensive, easy to handle, and genetically tractable. For this study, we used Wild Type strain BY4741, and a ?Hog1 strain based on the parental strain. Hog1 is a protein kinase involved in sensing cell stress and maintaining cell wall integrity. Wild Type and ?Hog1 strains were exposed to 500 ppm-1000 ppm of ZnO NPs in both NG and MMG conditions. Our results show that in NG conditions, both wild type and ?Hog1 strains have under 10.00% cell survival when exposed to 500 and 1000 ppm ZnO NPs. In MMG conditions, ZnO NPs lose their microbicidal properties: We observed around 80.00% cell survival at 500 ppm in the Wild Type strain. However, under the same conditions, the ?Hog1 strain only has < 5.00% cell survival. We conclude that ZnO NPs lose their microbicidal activities in MMG conditions, and that Hog1 protein is necessary for the reduced cytotoxicity observed under modeled microgravity conditions. This phenomenon could have vast implications for human health during spaceflight. Future research involves studying changes in ZnONPs/cell interactions, differences in the creation of ROS, and measuring changes in cell wall integrity during NG vs. MMG conditions.