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Title:Bacterial adhesion and detachment from model mineralized biofilms
Author(s):Carmichael, Ariel L
Department / Program:Civil & Environmental Eng
Discipline:Environ Engr in Civil Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Degree:M.S.
Genre:Thesis
Subject(s):biofilm
mineralization
calcite
elasticity
agarose
Abstract:Pathogen outbreaks have been linked to drinking water distribution systems (DWDSs), where the pathogens have been found to be harbored in biofilm layers inaccessible to disinfectants. Biofilm growth is ubiquitous in both natural and engineered environments, including the pipe networks of DWDSs. Calcium carbonate is also often found precipitated on pipe walls and biofilms, but the influence of its presence on the interaction between biofilms and pathogens is still unknown. The objective of this study is to determine the influence of calcium carbonate precipitates on pathogen adhesion to and detachment from biofilms. Thus far, the research focus has been to create an agarose hydrogel with similar elastic moduli to real biofilms in order to perform systematic studies of calcium carbonate precipitation within the gel. Agarose is a polymer made of chains of alternating galactose and anhydrous galactose, whose elastic modulus can be tuned by varying the agarose content. Thermogravimetric analyses (TGA), confocal microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy (FTIR) have been used to elucidate composition of mineralized gels and response to mineralization. Our findings show that the only crystalline phase within the agarose hydrogels is calcite and that the crystals sit in one main layer. Based on the TGA results, increasing concentrations of calcium ions appear to weaken the hydrogel structure, though this effect is less significant in the mineralized gels, where the calcium is consumed by precipitation of calcite. The agarose content within the calcite crystals was found to be between 5.4-10.6%, which is not negligible. Atomic force microscopy (AFM) microindentation was used to study the viscoelasticity of non-mineralized and mineralized hydrogels to increase understanding of how crystallization affects the polymer network’s structure and the mechanical behavior. Elastic moduli of the non-mineralized gels had a wide range of values (averages from 0.52-3.87 kPa), but results were reproducible within replicates. The influence of mineralization on the local mechanical properties of the agarose gel appears to be small, suggesting that although gelation happens at different concentrations, the network equilibrates to the same calcium concentration in saturated calcium carbonate solution. This finding excludes one mineralized gel that had increased moduli in areas within a cluster of crystals, which could not be attributed to substrate effects alone. The deviation between replicates is attributed mostly to small changes in water content, resulting in significant changes in the elastic modulus. Elastic moduli of biofilms were found to be even lower (averaging 0.16 kPa), but these results may not be reliable due to colloidal probe roughness and biofilm thickness. While the colloid roughness leads to an underestimation of the elastic moduli, small biofilm thickness may enhance substrate effects, thereby causing an overestimation of the stiffness. Further studies to understand the role of calcium ions and of local heterogeneities in the agarose hydrogels include AFM microindentation on non-mineralized gels in deionized water and calcium-enhanced gels, and macro-rheology experiments on non-mineralized, mineralized, and calcium-enhanced gels, respectively. We will also extend the work to real bio-mineralized biofilms and to measurements of adhesion between model biofilms and colloidal particles and bacteria as a function of the mineral content.
Issue Date:2016-04-26
Type:Thesis
URI:http://hdl.handle.net/2142/90941
Rights Information:Copyright 2016 Ariel Carmichael
Date Available in IDEALS:2016-07-07
Date Deposited:2016-05


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