Steven W. Peretti

Coordinated clearance of periciliary liquid and mucus from airway surfaces.

Airway surface liquid is comprised of mucus and an underlying, watery periciliary liquid (PCL). In contrast to the well-described axial transport of mucus along airway surfaces via ciliary action, theoretical analyses predict that the PCL is nearly stationary. Conventional and confocal microscopy of fluorescent microspheres and photoactivated fluorescent dyes were used with well-differentiated human tracheobronchial epithelial cell cultures exhibiting spontaneous, radial mucociliary transport to study the movements of mucus and PCL. These studies showed that the entire PCL is transported at approximately the same rate as mucus, 39.2+/-4.7 and 39.8+/-4.2 micrometer/sec, respectively. Removing the mucus layer reduced PCL transport by > 80%, to 4.8+/-0.6 micrometer/sec, a value close to that predicted from theoretical analyses of the ciliary beat cycle. Hence, the rapid movement of PCL is dependent upon the transport of mucus. Mucus-dependent PCL transport was spatially uniform and exceeded the rate expected for pure frictional coupling with the overlying mucus layer; hence, ciliary mixing most likely accelerates the diffusion of momentum from mucus into the PCL. The cephalad movement of PCL along airway epithelial surfaces makes this mucus-driven transport an important component of salt and water physiology in the lung in health and disease.

Safety and tolerability considerations: tricyclic antidepressants vs. selective serotonin reuptake inhibitors

Peretti S, Judge R, Hindmarch I. Safety and tolerability considerations: tricyclic antidepressants vs. selective serotonin reuptake inhibitors. Acta Psychiatr Scand 2000: 101: 17–25.

Removal of p-nitrophenol from aqueous solution by membrane-supported solvent extraction

Abstract p-Nitrophenol was extracted from aqueous solution into 1-octanol via membrane solvent extraction, using a hydrophobic, microporous-wall, polypropylene hollow fiber module. The system was operated with the aqueous phase flowing through the fiber lumens and the octanol flowing through the shell space. The overall mass transfer coefficient for the extraction was measured and analyzed in terms of individual resistance to mass transfer. The average value for the overall mass transfer coefficient was 6.5×10−4 cm/sec. The resistance to mass transfer of the tube side boundary layer and membrane were found to be controlling, while the shell side boundary layer resistance was negligible. The tube side boundary layer resistance measured in these experiments agreed well with a prediction based on the Sherwood number correlation for well developed laminar flow in tubes. The experimentally measured membrane permability to solute transport was substantially smaller than that predicted for solute diffusion through octanol occupying the membrane pores; flow maldistribution and channeling of solvent in the shell space is believed to be the most probable cause of this disparity. The results support the belief that membrane solvent extraction may be a technically and economically feasible means for selectively removing organic solutes from very dilute aqueous waste streams characteristic of many chemical plant effluents.

Studies of host-plasmid interactions in recombinant microorganisms

Plasmid genes redirect some components of cellular metabolism into synthesis of plasmid gene products and additional plasmids. The stoichiometric and kinetic implications of these host-plasmid interactions have been investigated theoretically and experimentally. Using known pathway energetics, maximum theoretical yield factors based on ATP, glucose, and O2 have been estimated for recombinant Escherichia coli and compared with corresponding estimates for host cells alone, indicating major changes in carbon and energetic stoichiometry in recombinant cells in cases of high cloned gene expression. The influence of the number of plasmids in recombinant E. coli has been experimentally characterized using a series of pMB1 derivatives stably propagated at copy numbers from 12 to 408. Recombinant cell growth rate declines monotonically as plasmid content increases as does efficiency of plasmid gene expression. A detailed metabolically structured single-cell model for E. coli has successfully simulated these trends. Interrelationships among number of plasmids per cell, induction of expression of a plasmid gene, and recombinant population growth rate have been experimentally delineated for Saccharomyces cerevisiae containing plasmid pLGSD5 and derivatives in which the 2-micron origin of replication has been replaced by a cloned ARS1 sequence or its deletion fragments. The CEN4 centromere sequence has been included in some of these plasmids to provide more regular segregation. Specific growth rate of these recombinant yeasts exhibits a maximum as a function of plasmid content, an effect attributed to the interplay between beneficial effects of the plasmid in selective medium and parasitic effects on metabolism at larger plasmid content or with more plasmid gene expression activity. The yeast strains investigated exhibit substantial segregational instability that was characterized using a rapid-flow cytometry measurement based upon single-cell deletion of E. coli beta-galactosidase activity in recombinant cells.

Challenges in Learning Communication Skills in Chemical Engineering.

Communication across the curriculum initiatives face multiple curricular and pedagogical challenges that are especially appropriate for investigation within a scholarship of teaching and learning framework. Using qualitative methodologies, this study examined technical classes that emphasize speaking and writing. Four learning issues emerged in student reflection logs: integrating multidisciplinary information, managing varied audiences and feedback, aligning content and communication tasks, and addressing interpersonal team issues. Data indicated that students were resistant toward the incursion of communication in their engineering classes. Through reflective practice, teachers and cross-curricular consultants came to understand and address that resistance.

Extraction of 4-nitrophenol from 1-octanol into aqueous solution in a hollow fiber liquid contactor

Abstract p -Nitrophenol (PNP) was extracted from 1-octanol into an aqueous buffered solution using membrane-supported extraction in hollow fiber liquid contactors (HFLCs) containing hydrophobic, microporous polypropylene fibers. PNP is a weak acid and in aqueous solution may dissociate to form nitrophenolate ion (PNP − ), that has negligible solubility in 1-octanol. The ratio of the two species in aqueous solution is governed by pH; therefore, the overall mass transfer coefficient based on solvent phase concentrations was determined as a function of pH. The extraction of PNP is a four-step process, consisting of diffusion across the solvent boundary layer, diffusion through the solvent-filled membrane, reaction (dissociation) at the solvent/aqueous interface, and diffusion across the aqueous boundary layer. The reaction step is assumed much faster than the others; a model of the mass transfer capabilities of the system is presented based on this assumption. The overall mass transfer coefficients were determined experimentally by recirculating the solvent phase through the shell space of a HFLC and the aqueous phase through the fibers. The model closely predicts the experimentally measured trends of the overall mass transfer coefficient.

Enhanced plasmid stability through post-segregational killing of plasmid-free cells

In order to develop an extremely stable, inducible host/vector system, the following genetic manipulations were made: a recA mutation was introduced into the chromosome of the host strain, the plasmid selectable marker was changed from ampicillin to kanamycin, and the parB stability locus of plasmid R1 was added to the plasmid. The stability of the new vector, pTKW106, was increased such that the fraction of plasmid-bearing cells present during chemostat fermentations under selective pressure increased from 1.75% to 100% when plasmid protein production was fully induced. At this level of induction, β-galactosidase represents 10% of the total cell protein. In addition, the frequency of generation of plasmid-free cells was shown to decrease from 1.0 per generation to less than 10−11 with full promoter induction under non-selective conditions.

Mobilization of broad host range plasmid from Pseudomonas putida to established biofilm of Bacillus azotoformans. I. Experiments.

A strain of Pseudomonas putida harboring plasmids RK2 and pDLB101 was exposed to a pure culture biofilm of Bacillus azotoformans grown in a rotating annular reactor under three different concentrations of the limiting nutrient, succinate. Experimental results demonstrated that the broad host range RSF1010 derivative pDLB101 was transferred to and expressed by B. azotoformans. At the lower concentrations, donor mediated plasmid transfer increased with increasing nutrient levels, but the highest nutrient concentration yielded the lowest rate of donor to recipient plasmid transfer. For transconjugant initiated transfer, the rate of transfer increased with increasing nutrient concentrations for all cases. At the lower nutrient concentrations, the frequency of plasmid transfer was higher between donors and recipients than between transconjugants and recipients. The reverse was true at the highest succinate concentration. The rates and frequencies of plasmid transfer by mobilization were compared to gene exchange by retrotransfer. The initial rate of retrotransfer was slower than mobilization, but then increased dramatically. Retrotransfer produced a plasmid transfer frequency more than an order of magnitude higher than simple mobilization.

Operation of mixed-culture immobilized cell reactors for the metabolism of meta- and para-nitrobenzoate by comamonas sp. JS46 and comamonas sp. JS47

The treatment of meta- and para-nitrobenzoic acid in an industrial wastestream by Comamonas sp. JS46 and Comamonas sp. JS47 is investigated. The most important feature of the wastestream is the constantly changing concentration ratio of the two isomers. The most extreme occurrence is considered here: the complete change in feed carbon source from one isomer to the other. A series of immobilized cell airlift reactor experiments are described to examine the operation and response of the system to these changes in the feed carbon source. Separate reactors containing each species immobilized are compared with a reactor containing both species immobilized within the same bead, and to a reactor containing both species with each species confined to separate beads. On the basis of response time necessary to recover the appropriate activity, the reactor containing both species immobilized within the same bead offers the most effective arrangement. Interactions occurring between the two organisms in the coimmobilized system, mediated by the nitrobenzoate metabolites, are discussed relative to the improved response of this arrangement. Copyright 1998 John Wiley & Sons, Inc.

Use of flow cell reactors to quantify biofilm formation kinetics

A parallel plate flow cell reactor is introduced and used to evaluate cell adhesion and biofilm formation kinetics for four different bacterial strains of the species,E. coli. The reactor allows biofilm growth under defined, well-controlled fluid dynamics while providing continuous observations and direct sampling of biofilm for biological, chemical and physical analyses as well as immunofluorescent labeling.