Matching Items (3)
Description
Bacterial biofilms exist on surfaces within pressurized water systems, posing threats to water quality and causing fouling or microbial induced corrosion. Germicidal UV irradiation has shown promise in deactivating planktonic pathogens in water but challenges in delivering light to surfaces where biofilms exist have limited advancement in understanding biofilm response to UV-C light. This dissertation aims to overcome the limitation of delivering UV-C light through use of side-emitting optical fibers (SEOFs), advance capabilities to produce SEOFs and understand if a minimum UV-C irradiance can prevent biofilm formation. Two scalable manufacturing approaches were developed for producing kilometer lengths of thin (≤500-µm) and physically flexible SEOFs. One strategy involved dip-coating amine-functionalized SiO2 nanoparticles (NPs) on bare optical fiber, followed by a coating of UV-C transparent polymer (CyTop). I showed that NPs closer to the surface achieved with higher ionic strength solutions increased side-scattering of UV-C light. This phenomenon was primarily attributed to the interaction between NPs and evanescent wave energy. The second strategy omitted NPs but utilized a post-treatment to the UV-C transparent polymer that increased surface roughness on the outer fiber surface. This modification maintained the physical flexibility of the fiber while promoting side-emission of UV-C light. The side emission was due to the enhancement of refracted light energy. Both methods were successfully scaled up for potential commercial production.
Experimental platforms were created to study biofilm responses to UV light on metal or flexible plastic pipe (1/4” ID) surfaces. Delivering UV-C light via SEOFs with irradiances >8 µW/cm2 inhibited biofilm accumulation. Neither UV-A nor UV-B light inhibited biofilm growth. At very low UV-C irradiance (<3 µW/cm2), biofilms were not inhibited. Functional genomic analysis revealed that biofilms irradiated by insufficient UV-C irradiance upregulated various essential genes related to DNA repair, energy metabolism, quorum sensing, mobility, and EPS synthesis. When net UV-C biofilm inactivation rates exceeded the biofilm growth rate, biofilms were inhibited. Insights gained from this dissertation work shed light on the prospective applications of UV-C technology in addressing biofilm challenges within water infrastructure across multiple sectors, from potable water to healthcare applications.
ContributorsZhao, Zhe (Author) / Westerhoff, Paul (Thesis advisor) / Rittmann, Bruce (Committee member) / Abbaszadegan, Morteza (Committee member) / Álvarez, Pedro (Committee member) / Arizona State University (Publisher)
Created2023
Description
Scientific researchers have studied microorganisms since the emergence of the single lens microscope in the 17th century. Since then, researchers designed and published many thousands of images to record and share their observations, including hand-drawn diagrams, photomicrographs, and photographs. Images shaped how researchers conceived of microorganisms, their concepts of microorganisms shaped their images, and their images and concepts were shaped by the contexts in which they were working. Over time, the interplay of images and concepts in various research contexts participated in the development of new concepts related to microorganisms, like the “biofilm” concept, or the idea that bacteria exist in nature as complex aggregates attached to surfaces via extracellular polymeric matrices. Many histories of microbiology locate the origin of the biofilm concept in the 1970s, but that date obscures the rich history of research about attached microbial aggregates that occurred throughout the history of microbiology. I discovered how the interplay of images and concepts related to bacteria participated in the development of the biofilm concept by documenting when and why researchers used different visual features to represent changing concepts related to microorganisms. I specifically examined how and why scientists represented evolving concepts related to bacteria during the 17th century (Chapter 1), from the late 17th century to the early 20th century (Chapter 2), and during the first seventy-four years of the 20th century (Chapter 3). I discovered the biofilm concept developed in at least three unique research contexts during the 20th century, and how images reflected and shaped the concept’s development in each case. The narrative and collection of images generated from this work serve as a visual history of the development of scientists’ ideas about the nature of bacteria over 300 years.
ContributorsGuerrero, Anna Clemencia (Author) / Maienschein, Jane (Thesis advisor) / Laubichler, Manfred (Committee member) / Sterner, Beckett (Committee member) / Matlin, Karl (Committee member) / Arizona State University (Publisher)
Created2023
Description
This study investigated the difference in biofilm growth on pristine and aged polypropylene microplastics exposed to Tempe Town Lake water for 8 weeks. The research question here is, does the aging of microplastic (MPs) change the biofilm formation rate and composition of the biofilm in comparison with the pristine MPs. To answer this question, the biofilm formation was quantified using different methods over time for both pristine polypropylene and aged polypropylene using agar plate counts and crystal violet staining. Colony counts based on agar plating showed an increase in microbial growth over the 8 weeks of treatment, with the aged MPs accumulating higher microbial counts than the pristine MPs. The diversity of the biofilm decreased over time for both MPs and the aged MPs had overall less diversity in biofilm, based on phenotype enumeration, in comparison with the pristine MPs. Higher biofilm growth on aged MPs was confirmed using crystal violet staining, which stains the negatively charged biological compounds such as proteins and the extracellular polymeric substance matrix of the biofilm. Using this complementary approach to colony counting, the same trend of higher biofilm growth on aged MPs was found. Further studies will focus on confirming the phenotype findings using microbiome analysis following DNA extraction. This project created a methodology to quantify biofilm formation on MPs, which was used to show that MPs may accumulate more biofilms in the environment as they age under sunlight.
ContributorsMushro, Noelle (Author) / Perreault, Francois (Thesis advisor) / Hamilton, Kerry (Committee member) / Krajmalnik-Brown, Rosa (Committee member) / Arizona State University (Publisher)
Created2022