Date of Award
Doctor of Philosophy in Civil and Environmental Engineering
Civil and Environmental Engineering
Vinka Oyanedel Craver
Bacteria have the extraordinary capability to modify their phenotype in response to stress agents. Response mechanisms to stressor (such as nanoparticles or light treatments) are the result of an evolutionary process in which bacteria can become resistant, or adapt to the stressor. Therefore, it is essential to elucidate the bacterial adaptation mechanisms to metal nanoparticles or pulse ultraviolet light since these processes not only can compromise the efficacy of these treatment methods but also has implications to public health issues.
Silver nanoparticles (AgNPs) are one of the most commonly used nanomaterials in consumer products and medical applications due to their antimicrobial properties. Also, pulsed lights (PL) applications for water treatment purposes are gaining increasing attention. PL has showed higher inactivation of microorganisms and degradation of PAHs, because of its rich and broad-spectrum UV content, high energy peaks and predictable treatment outcomes. However, the fate of microorganisms after exposure to AgNPs and pulsed lights as well as their negative impacts possible on the environment and public health are growing concerns.
There are knowledge gaps related to: the studying molecular level change of microorganism after exposure to AgNPs by Fourier-transform infrared spectroscopy (FTIR); Bacterial adaptation to chronic exposure to nanoparticles in continuous culture: kinetic and macromolecular response; and the effect of pulsed ultraviolet light system for removal of polycyclic aromatic hydrocarbon and disinfection of pathogens in drinking water.
In this study, Escherichia coli K-12 MG1655 (E. coli) responses to AgNPs was assessed under batch and continuous conditions. Further, we investigated the response of the same bacteria to PL. In detail, we evaluated antimicrobial agent’s impacts on metabolic functions and cell structure such as, colony formation units, membrane permeation, respiration, growth, gene regulation and changes in cellular composition.
The results of batch culture for AgNPs toxicity test showed that bacteria developed resistance toward AgNPs and resulted in changes in the genotype and expression in the phenotype. Moreover, in continuous culture, results showed that culture growth conditions significantly affect bacterial response to nanoparticle exposure. Finally, from PL exposure to bacteria we obtained that the antimicrobial efficiency of PL depends on the PL lamp cut-off.
This study provides data that have a predominant role to determine the performance of toxicological tests. Hence, the knowledge of nanoparticles fate in different growth condition minimizes the upcoming environmental and public health issues due to releasing nanoparticles release on the ecosystems. Also, understanding the bacterial responses to antimicrobial agents help us to select the more sensible agents for antimicrobial purposes.
Faghihzadeh, Fatemeh, "Kinetic, Metabolic and Macromolecular Response of Bacteria to Antimicrobial Agents" (2018). Open Access Dissertations. Paper 723.