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To reduce reliance on fossil fuels, sustainable biofuels are being pursued, especially advanced biofuels like 1-butanol that have higher energy content and greater compatibility with existing infrastructure than ethanol. A persistent challenge is the yield-limiting toxicity of biofuels and process solvents, such as tetrahydrofuran, to the microbes that ferment biomass into biofuel. The cell membrane is a focal point of toxicity, and understanding how it interacts with fuels and solvents is key to improving yield. Phospholipid bilayers are the core of biomembranes, and model biomembranes of defined composition provide the ideal platform for biophysical studies. To this end, glycerophospholipids characteristic of Bacillus subtilis, a model producer organism, were synthesized. Two fatty acids (iso- and anteisopentadecanoic acids) characteristic of Bacilli were synthesized and incorporated into representative phosphatidic acid, phosphatidylethanolamine and phosphatidylglycerol lipids. The validated synthetic approach opens the door to future studies on the interaction of biofuels and solvents with biomembranes.

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No description available.

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This research first examined nitrification inhibition caused by different classes of industrially relevant chemicals on activated sludge and found that conventional aerobic nitrification was inhibited by single pulse inputs of every chemical tested, with 1-chloro-2,4-dinitrobenzene (oxidant) having the most severe impact, followed by alkaline pH 11, cadmium (heavy metal), cyanide, octanol (hydrophobic) and 2,4-dinitrophenol (respiratory uncoupler). Of the different chemicals tested, the oxidative and hydrophobic chemicals showed severe nitrification inhibition relative to other treatment processes and therefore deserved further investigation. For oxidative chemicals, we hypothesized that the more severe inhibition was because nitrifying bacteria lack one or more of the microbial stress response mechanisms used to mediate the toxic effect of oxidative chemicals. During these experiments, we showed that a rapid (minutes) antioxidant potassium efflux mechanism does not exist in two nitrifying bacteria, Nitrosomonas europaea and Nitrospira moscoviensis. Furthermore, we showed that another important antioxidant molecule, glutathione, was not oxidized as readily as in a non-nitrifying bacterium. Furthermore, we hypothesized that hydrophobic chemical-induced nitrification inhibition recovered more quickly because of the presence of membrane modification stress response mechanisms. While testing this hypothesis, we showed that N. europaea modified its cell membrane in response to hydrophobic chemicals using a long-term (hours) membrane modification mechanism that required the synthesis of new fatty acids, but it did not contain a short-term (minutes) response mechanism involving a cis/trans isomerase. Therefore, investigating these nitrifier stress responses showed that nitrifiers lack short-term stress responses that may be used to rapidly detect inhibition, indicating that conventional methods of detecting nitrification inhibition, like differential respirometry and nitrate generation rate (NGR), are still the fastest and easiest methods to use. Because several conventional methods exist, we also investigated differences between differential respirometry and a UV method we developed to measure NGR. During these tests, we showed that the UV NGR method provided a more reliable measure of nitrification inhibition than differential respirometry, and that the time to maximum nitrification inhibition depended on the properties of the chemical toxin, which implies that longer exposure times may be needed to accurately predict nitrification inhibition. / Ph. D.

Hair cell structures are one of the most common forms of sensing elements found in nature. In humans, approximately 16,000 auditory hair cells can be found in the cochlea of the ear. Each hair cell contains a stereocilia, which is the primary structure for sound transduction. This study looks to develop and characterize a bilayer lipid membrane (BLM) operated artificial hair cell sensor that resembles the stereocilia of the human ear. To develop this sensor, a flexible substrate with internal compartments for hosting the biomolecules and mating cap are constructed and experimentally characterized. The regulated attachment method (RAM) is used to form bilayers within the sealed device. Capacitance measurements of the encapsulated bilayer show that the sealing cap slightly compresses the bottom insert and reduces the size of the enclosed bilayer. Single channel measurements of alamethicin peptides further verify that the encapsulated device can be used to detect the gating activity of transmembrane proteins in the membrane. The flexible substrate was incorporated into a low-noise, portable test fixture. The response of the sensor and tip velocity of the hair were measured with respect to an impulse input on the test fixture and several frequency response functions (FRFs) were created. The FRF between the sensor and the tip velocity was used to show that the hair vibration was transmitted to the bilayer for certain hair lengths. The transfer function between the sensor and the input was used to show the effect of membrane potential on sensor response. / Master of Science

Thesis (Ph. D.)--University of Virginia, 2008. / Title from title page. Includes bibliographical references. Also available online through Digital Dissertations.