Recent data indicate that cystic fibrosis (CF) airway mucus is anaerobic. This suggests that Pseudomonas aeruginosa infection in CF reflects biofilm formation and persistence in an anaerobic environment. P. aeruginosa formed robust anaerobic biofilms, the viability of which requires rhl quorum sensing and nitric oxide (NO) reductase to modulate or prevent accumulation of toxic NO, a byproduct of anaerobic respiration. Proteomic analyses identified an outer membrane protein, OprF, that was upregulated approximately 40-fold under anaerobic versus aerobic conditions. Further, OprF exists in CF mucus, and CF patients raise antisera to OprF. An oprF mutant formed poor anaerobic biofilms, due, in part, to defects in anaerobic respiration. Thus, future investigations of CF pathogenesis and therapy should include a better understanding of anaerobic metabolism and biofilm development by P. aeruginosa.

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Publication costs assisted by the Petroleum Research Fund A detailed analysis of line shapes and relaxation is made for the perdeuterated 2,2,6,6-tetramethyl-4-piperidone AT-oxide (PD-Tempone) nitroxide radical covering the whole range from fast motional narrowing (tr ~10-12 sec) to the rigid limit (tr ~10-6 sec) in several deuterated solvents. The slow tumbling resultsshow particularly good agreement with the slow tumbling theory of Freed, et ai, for a reorientational model of moderate jumps (ca. 50°r ms), and essentially isotropic reorientation. It is shown that while such a model may not be readily distinguished, purely from its slow tumbling spectral predictions, from a free diffusion model including inertial effects, the latter model is incompatible with most other considerations. However, a simple analysis explicitly including the fluctuating (or random) torques indicates that more fundamental analysis of the dynamics may explain the slow tumbling results without necessarily involving substantial jumps. The spectral analysis is considerably enhanced by the increased resolution obtained from the use of the perdeuterated spin probe and deuterated solvents. Careful analysis of results at X-band and 35 GHz has shown that the nonsecular spectral densities exhibit significant deviations from a Debyelike spectral density yielding results very similar to those recently reported for the peroxylaminedisulfonate (PADS) radical. Related observations are discussed of apparent non-Debye-like spectral densities in the incipient slow tumbling spectra. These anomalies are also found to be amenable to a unified explanation in terms of the fluctuating torques. The analysis of much of the results in terms of a simple model yields an rms value for the fluctuating torques of ca, V6kT and tm ~tr where tm is the relaxation time of the torques. The high-temperature electron-spin flip processes are consistent with a Hubbard-type spinrotational mechanism, but the low-temperature results may be due to spin-rotational relaxation from intramolecular motions. The simple analysis of spin-rotational relaxation in terms of relaxation of the fluctuating torques is found to yield equivalent predictions to conventional treatments when the estimated values of rms torque and tm are used.

Nano-sized titanium dioxide (TiO2) is among the top five widely used nanomaterials for various applications. In this study, we determine the phototoxicity of TiO2 nanoparticles (nano-TiO2) with different molecular sizes and crystal forms (anatase and rutile) in human skin keratinocytes under UVA irradiation. Our results show that all nano-TiO2 particles caused phototoxicity, as determined by the MTS assay and by cell membrane damage measured by the lactate dehydrogenase (LDH) assay, both of which were UVA dose- and nano-TiO2 dose- dependent. The smaller the particle size of nano-TiO2 the higher the cell damage. The rutile form of nano-TiO2 showed less phototoxicity than anatase nano-TiO2. The level of photocytotoxicity and cell membrane damage is mainly dependent on the level of reactive oxygen species (ROS) production. Using polyunsaturated lipids in plasma membranes and human serum albumin as model targets, and employing electron spin resonance (ESR) oximetry and immuno-spin trapping as unique probing methods, we demonstrated that UVA irradiation of nano-TiO2 can induce significant cell damage, mediated by lipid and protein peroxidation. These overall results suggest that nano-TiO2 is phototoxic to human skin keratinocytes, and that this phototoxicity is mediated by ROS generated during UVA irradiation.