Nanoparticles Toxicity on \u3cem\u3eEscherichia coli\u3c/em\u3e: Batch and Kinetic Approach

Silver and dysprosium oxide are two examples of materials used for the manufacturing of nanoparticles with current and future commercial relevance, respectively. Silver nanoparticles (nAg or AgNPs) are one of the most commonly used nanomaterials in consumer products and medical applications due to their antimicrobial properties. Dysprosium oxide nanoparticles (nDy2O3) are gaining interest for biomedical applications because of their fluorescence and paramagnetic properties, which can be used as contrast agents in magnetic resonance analysis. However, the fate of nAg and nDy2O3 and their possible negative impacts on the environment and public health are growing concerns. Nanoparticles entering and accumulating in different environmental compartments will very likely interact with native bacteria in soil and aquatic environments. There are knowledge gaps related to: the exposure of novel nanomaterials on microorganisms in different water chemistry conditions; the effect of reactor configuration to assess nanotoxicology; and the effect of the specific growth rate on the response of microorganisms exposed to nanoparticles. In this study, nanoparticles toxicity on Escherichia coli (E. coli) was assessed under batch and continuous conditions, and evaluated their impacts on metabolic functions and cell structure such as, viability, membrane permeation, respiration, growth and changes in intracellular composition. The results showed that several methodologies are needed to obtain a comprehensive understanding of the toxicological of the exposure of nanoparticles on microorganisms. At growing conditions, chemostat systems can provide a better assessment of the nanoparticle inhibitory effects on microorganisms in comparison to batch systems. However, there is not control of the contact time and the specific growth rate and contact time effects are combined. Longer term exposure and chronic studies are suggested to separate the growth rate effect from the contact time. The data produced during this study is relevant to determine the real world implications on ecosystems and public health when the nanoparticles are released into the environment. With an understanding of the fate of nanoparticles in aqueous media, a more careful selection of toxicological methodologies and testing conditions can be made. This will allow for more accurate studies that measure the responses of microorganisms to the exposure of nanoparticles