Effect of silver nanoparticles on planktonic and biofilm cell growth

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb. 23, 2010).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Dissertation advisor: Dr. Zhiqiang Hu.Vita.Includes bibliographical references.Ph. D. University of Missouri--Columbia 2009.Dissertations, Academic -- University of Missouri--Columbia -- Civil engineering.Silver nanoparticles (Ag NPs) are one of the most widely used nanoparticles, most notably serving as an antimicrobial agent for sanitization and medical purposes. Despite of their widespread use, little was known about the environmental effect of silver nanoparticles. This research focused on the impact of AgNPs on planktonic (e.g., free swimming) and biofilm bacteria that are relevant to wastewater treatment and the natural environment. Nitrifying bacteria and E. coli were used as model microorganisms because they are essential in nitrification processes and a good water quality indicator in the environment, respectively. Ag NPs were prepared in the lab and fully characterized by analyzing their optical property, size distribution, and composition (Ag⁺/Ag NPs). Several microbial toxicity tests (autotrophic respirometry, GFP-fluorescence microtiter assay, and oxygen based microrespirometry) were developed and applied individually depending on the microbial growth conditions. The research results demonstrated that the toxicity of Ag NPs was dependent on nanosilver particle sizes and related to of the concentration of intracellular reactive oxygen species (ROS). However, other metallic/oxide particles such as TiO₂ nanoparticles showed lower toxicity than Ag NPs to the microorganisms with higher ROS accumulation, indicating that ROS was not a good chemical marker to determine the toxicity of metallic nanoparticles. To control the toxicity by metallic nanoparticles such as Ag NPs, sulfide anion effectively reduced the nanotoxicity because of the formation of stable Ag[subscript-x]S[subscript-y] complex as a result of nanosilver dissolution and silver-sulfide complexation. E. coli biofilm cells were more resistance to the toxicity of Ag NPs than the planktonic cells. To determine the relationship between the toxicity and the fate of nanosilver in biofilms, the spatial distribution of Ag NPs in biofilms was analyzed using E. coli expressing green fluorescent protein (GFP) and the indigenous red fluorescence of aggregated silver particles. The results suggested that biofilms might confer resistance to nanosilver through particle aggregation and retarded Ag⁺/Ag NPs diffusion

Caprylate production with lactate as electron donor using Megasphaera hexanoica

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Enhanced extraction of butyric acid under high-pressure CO2 conditions to integrate chemical catalysis for value-added chemicals and biofuels

Abstract Background Extractive fermentation with the removal of carboxylic acid requires low pH conditions because acids are better partitioned into the solvent phase at low pH values. However, this requirement conflicts with the optimal near-neutral pH conditions for microbial growth. Results CO2 pressurization was used, instead of the addition of chemicals, to decrease pH for the extraction of butyric acid, a fermentation product of Clostridium tyrobutyricum, and butyl butyrate was selected as an extractant. CO2 pressurization (50 bar) improved the extraction efficiency of butyric acid from a solution at pH 6, yielding a distribution coefficient (D) 0.42. In situ removal of butyric acid during fermentation increased the production of butyric acid by up to 4.10 g/L h, an almost twofold increase over control without the use of an extraction process. Conclusion In situ extraction of butyric acid using temporal CO2 pressurization may be applied to an integrated downstream catalytic process for upgrading butyric acid to value-added chemicals in an organic solvent

The distribution of major classes of the bacterial community.

<p>Diverse bacteria were present, and it was expected that they played a role in acetate consumption.</p

Abundance in the total community of major metanogenic species.

<p>Double pie chart shows major classes (inner) and species (outer). Mainly methanobacteria are present.</p