Abstract: Engineered nanomaterials (ENMs) can alter surface properties of cells and disturb cellular functions and gene expression through direct and indirect contact, exerting unintended impacts on human and ecological health. However, the effects of interactions among environmental factors, such as light, surrounding media, and ENM mixtures, on the mechanisms of ENM toxicity, especially at sublethal concentrations, are much less explored and understood. Recent studies have shown that nanoparticles can facilitate bacteriophage infection which contributes to transduction, an understudied yet crucial pathway of antibacterial gene transfer in bacteria. Therefore, we first evaluated cell viability and outer membrane permeability of E. coli as a function of exposure to environmentally relevant concentrations of ENMs, including metal (n-Ag) and metal oxide (n-TiO2, n-Al2O3, n-ZnO, n-CuO, and n-SiO2) nanoparticles under dark and simulated sunlight illumination in MOPS, a synthetic buffer, and Lake Michigan Water (LMW), a freshwater medium. Then we investigated the effects of photoactive ENMs on bacteriophage infection under sublethal concentrations and tried to unravel the mechanisms in gene expression associated with F-pili and membrane proteins. Our results reveal the significant sublethal bacterial stress exerted by ENMs and ENM mixtures at the cell surface in natural environments at low doses, which potentially affects cell susceptibility to toxicants and virus, such as phage infection and eventually causes unpredictable impacts on overall ecological health.

Bio: Shushan Wu is a 6th year PhD student in Professor Kimberly Gray's group. Her work unveils the sublethal bacterial stress exerted by engineered nanomaterials under environmental conditions using advanced biological techniques. Shushan graduated from Auburn University with a bachelor's degree in civil and environmental engineering before pursuing graduate studies at Northwestern University.