Doctor of Philosophy

dissertationEndocrine disruption in aquatic animals caused by treated wastewater effluent has been extensively studied. Endocrine disruption describes the alteration of normal endocrine functions due to exposure by endocrine disrupting chemicals (EDCs). Estrogenic activity was frequently detected in wastewater treatment effluent, fresh water, or sedimentation due to incomplete degradation of EDCs in the wastewater treatment facilities. These endocrine disruptors can be degraded by microorganisms but at time scales of a few days to a hundred days. Biological processes only can degrade EDCs to a limited degree as indicated in treatment plant mass balance studies. Microorganisms utilize oxidation enzymes to breakdown EDCs to lower toxic level products during wastewater treatment, while metal and drug resistance proteins interact with the biodegradation process by exporting chemicals out of the cell. This mechanism reduces EDCs' availability and contact time with oxidation enzyme, resulting higher extracellular contaminant concentrations. The objective of this research is to find out if drug resistant proteins contribute EDCs' biopersistence and lack of EDCs biodegradation in wastewater treatment. The substrates of drug resistant proteins were selected among various estrogenic chemicals including natural and synthetic estrogens, phytoestrogens, plasticizers, flame retardants, and nonionic surfactants. Besides steroids, the synthetic estrogen 17α-ethynylestradiol, phytoestrogens of nonylphenol, octylphenol, and plasticizer bisphenol-A are substrates of the major multidrug resistant proteins AcrAB-TolC in E. coli and MexAB-OprM in Pseudomonas aeruginosa. As endocrine disruptors enter the bacterium, they are exported from the cell, limiting their contact time with oxidizing enzymes. The enzyme oxygenase was employed in this study to remove these endocrine disruptors. The results showed that toluene dioxygenase degrades bisphenol-A efficiently. Both multidrug resistant and oxygenase genes were transformed into E. coli, and batch bioreactors were used to determine the biodegradation ability. The presence of a drug resistant protein reduced the degradation rate of bisphenol-A to 0.146 hours-1 from the rate of 0.184 hours-1 without a resistant protein. To find out which proteins function at environmentally relevant concentrations found in wastewater treatment plants and surface water, efflux and oxidation gene induction was measured. In E. coli, hormone-resistant genes acrB and yhiV and peroxidase katE were expressed the greatest; in Pseudomonas, ring cleavage oxygenases and certain drug-resistant genes were up-regulated in the presence of EDCs. To apply this study for water reclamation and wastewater treatment plants, the bacteria population was monitored, and endocrine disrupting chemicals analysis was performed. Biological treatment only removed 75% of E2 (17β-estradiol) equivalent estrogenic activity in the Central Valley Water Reclamation Facility in Salt Lake City, Utah. Meanwhile, drug resistant bacteria were detected in the effluent of this wastewater treatment plant after all treatment processes, including UV disinfection

Quantification of the influence of drugs on zebrafish larvae swimming kinematics and energetics

The use of zebrafish larvae has aroused wide interest in the medical field for its potential role in the development of new therapies. The larvae grow extremely quickly and the embryos are nearly transparent which allows easy examination of its internal structures using fluorescent imaging techniques. Medical treatment of zebrafish larvae can directly influence its swimming behaviours. These behaviour changes are related to functional changes of central nervous system and transformations of the zebrafish body such as muscle mechanical power and force variation, which cannot be measured directly by pure experiment observation. To quantify the influence of drugs on zebrafish larvae swimming behaviours and energetics, we have developed a novel methodology to exploit intravital changes based on observed zebrafish locomotion. Specifically, by using an in-house MATLAB code to process the recorded live zebrafish swimming video, the kinematic locomotion equation of a 3D zebrafish larvae was obtained, and a customised Computational Fluid Dynamics tool was used to solve the fluid flow around the fish model which was geometrically the same as experimentally tested zebrafish. The developed methodology was firstly verified against experiment, and further applied to quantify the fish internal body force, torque and power consumption associated with a group of normal zebrafish larvae vs. those immersed in acetic acid and two neuroactive drugs. As indicated by our results, zebrafish larvae immersed in 0.01% acetic acid display approximately 30% higher hydrodynamic power and 10% higher cost of transport than control group. In addition, 500 μM diphenylhydantoin significantly decreases the locomotion activity for approximately 50% lower hydrodynamic power, whereas 100 mg/L yohimbine has not caused any significant influences on 5 dpf zebrafish larvae locomotion. The approach has potential to evaluate the influence of drugs on the aquatic animal’s behaviour changes and thus support the development of new analgesic and neuroactive drugs

Observation of the ground-state-geometric phase in a Heisenberg XY model

Geometric phases play a central role in a variety of quantum phenomena, especially in condensed matter physics. Recently, it was shown that this fundamental concept exhibits a connection to quantum phase transitions where the system undergoes a qualitative change in the ground state when a control parameter in its Hamiltonian is varied. Here we report the first experimental study using the geometric phase as a topological test of quantum transitions of the ground state in a Heisenberg XY spin model. Using NMR interferometry, we measure the geometric phase for different adiabatic circuits that do not pass through points of degeneracy.Comment: manuscript (4 pages, 3 figures) + supporting online material (6 pages + 7 figures), to be published in Phys. Rev. Lett. (2010