Biomedical subjects

Kenneth F Reardon

Publications and source records attributed to Kenneth F Reardon.

17 recordsLinked to original sources

PubMed2007

Comparison of CE-SSCP and DGGE for monitoring a complex microbial community remediating mine drainage.

Capillary electrophoresis single-strand conformation polymorphism (CE-SSCP) is a promising high-throughput tool for profiling complex bioremediation communities, but has not been well characterized with respect to other methods such as denaturing gradient gel electrophoresis (DGGE). The purpose of this study was to compare CE-SSCP with DGGE with respect to: 1) overall representation of the community in terms of the dominant species identified and corresponding Shannon diversity indices; 2) reproducibility and resolution; and 3) artifacts, using a complex sulfate-reducing community remediating mine drainage as a model system. Some of the dominant microorganisms were detected by both methods, but there were also differences in the reported community compositions, and more phylogenetic groups were detected by CE-SSCP. CE-SSCP Shannon diversity indices were slightly higher than those determined from DGGE data, and differed in terms of the time point at which the community was reported to have the highest diversity. Both methods had high reproducibility, but CE-SSCP resolution was higher in terms of the total number of peaks resolved, reduced co-migration of distinct DNA sequences, and length and legibility of the DNA sequencing data of clones used to identify peaks. Ten double bands in the same lane representing the same species were found by DGGE, whereas only one such artifact was observed by CE-SSCP. Finally, less overall sample preparation and analysis time was required for CE-SSCP than for DGGE. The results suggest that CE-SSCP offers several advantages over DGGE, especially for high-throughput monitoring.

Bacteria↗

PubMed2006

Development of a fiber optic enzymatic biosensor for 1,2-dichloroethane.

There is a significant need for devices capable of measuring water contaminant concentrations in situ--continuously, rapidly, and without reagents, extraction, or other pretreatment. Toward this goal, we constructed and tested fiber optic biosensors for measurement of 1,2-dichloroethane (DCA) in aqueous solutions. The biocomponent was the haloalkane dehalogenase, DhlA, in whole cells of Xanthobacter autotrophicus GJ10. These cells were immobilized in calcium alginate on the tip of a fiber optic fluoresceinamine-based pH optode. The resulting biosensor could quantify DCA at 11 mg/l and had a linear response up to at least 65 mg/l. Total signal change was reached in 8-10 min, and measurements were reproducible (SE <9%). The sensor's small size, potential for remote operation, and low cost make it of interest for further development.

Biosensing Techniques↗

PubMed2006

Shotgun proteomics of cyanobacteria--applications of experimental and data-mining techniques.

Cyanobacteria are photosynthetic bacteria notable for their ability to produce hydrogen and a variety of interesting secondary metabolites. As a result of the growing number of completed cyanobacterial genome projects, the development of post-genomics analysis for this important group has been accelerating. DNA microarrays and classical two-dimensional gel electrophoresis (2DE) were the first technologies applied in such analyses. In many other systems, 'shotgun' proteomics employing multi-dimensional liquid chromatography and tandem mass spectrometry has proven to be a powerful tool. However, this approach has been relatively under-utilized in cyanobacteria. This study assesses progress in cyanobacterial shotgun proteomics to date, and adds a new perspective by developing a protocol for the shotgun proteomic analysis of the filamentous cyanobacterium Anabaena variabilis ATCC 29413, a model for N(2) fixation. Using approaches for enhanced protein extraction, 646 proteins were identified, which is more than double the previous results obtained using 2DE. Notably, the improved extraction method and shotgun approach resulted in a significantly higher representation of basic and hydrophobic proteins. The use of protein bioinformatics tools to further mine these shotgun data is illustrated through the application of PSORTb for localization, the grand average hydropathy (GRAVY) index for hydrophobicity, LipoP for lipoproteins and the exponentially modified protein abundance index (emPAI) for abundance. The results are compared with the most well-studied cyanobacterium, Synechocystis sp. PCC 6803. Some general issues in shotgun proteome identification and quantification are then addressed.

Computational Biology↗

PubMed2005

Microbial community activities during establishment, performance, and decline of bench-scale passive treatment systems for mine drainage.

Permeable reactive barrier (PRB) technology, in which sulfate-reducing bacteria (SRB) facilitate precipitation of metal sulfides, is a promising approach for remediation of sulfate- and metal-laden mine drainage. While PRBs are easily established, they often decline for reasons not well understood. SRB depend on or compete with multiple dynamic microbial populations within a PRB; as a result, performance depends on the changing PRB chemical composition and on succession and competition within the microbial community. To investigate these interactions, we constructed and monitored eight bench-scale PRBs to define periods of establishment, performance, and decline. We then conducted short-term batch studies, using substrate-supplemented column materials, on Days 0 (pre-establishment), 27 (establishment), 41 (performance), and 99 (decline) to reveal potential activities of cellulolytic bacteria, fermenters + anaerobic respirers, SRB, and methanogens. PRBs showed active sulfate reduction, with sulfate removal rates (SRR) of approximately 1-3 mol/m3/d, as well as effective removal of Zn2+. Potential activities of fermentative + anaerobic respiratory bacteria were initially high but diminished greatly during establishment and dropped further during performance and decline. In contrast, potential SRB activity rose during establishment, peaked during performance, and diminished as performance declined. Potential methanogen activity was low; in addition, SRB-methanogen substrate competition was shown not to limit SRB activity. Cellulolytic bacteria showed no substrate limitation at any time. However, fermenters experienced substrate limitation by Day 0, SRB by Day 27, and methanogens by Day 41, showing the dependence of each group on upstream populations to provide substrates. All potential activities, except methanogenesis, were ultimately limited by cellulose hydrolysis; in addition, all potential activities except methanogenesis declined substantially by Day 99, showing that long-term substrate deprivation strongly diminished the intrinsic capacity of the PRB community to perform.

Alkalies↗

PubMed2005

A novel, sensitive method for determining benzo[a]pyrene-diones using high-performance liquid chromatography with post-column zinc reduction.

A novel and sensitive high-performance liquid chromatography (HPLC) method was developed to analyze dione metabolites of benzo[a]pyrene (BaP). Because BaP-diones do not fluoresce, detection of low concentrations is difficult to achieve when analyzing these chemicals with a simple HPLC system. We developed a method to increase the detection sensitivities for BaP-diones using reduction by zinc after the chromatographic separation. A post-column zinc reducer was used to convert BaP-diones, in-line, to their corresponding fluorescent BaP-hydroquinones, which can be measured by fluorescence detection with high sensitivity. With 20-muL injections, the limits of detection for the BaP-diones tested (BaP-1,6-dione, BaP-3,6-dione, and BaP-6,12-dione) were all below 1.0 nM. In addition to the high detection sensitivity, this HPLC method provides a wide linear dynamic range for BaP-dione detection (1.0-220 nM). We also studied the extraction recovery of BaP-diones from recombinant human cytochrome P450 and epoxide hydrolase. To demonstrate the application of this method, the kinetics of BaP-dione formation was studied by incubating BaP with these recombinant enzymes. The present method enhances the detection sensitivity for BaP-diones by more than two orders of magnitude compared with traditional ultraviolet detection. Moreover, the method avoids the time-consuming derivatization or reduction steps required by other methods.

Benzo(a)pyrene↗

PubMed2005

Hydroxyl free radical reactivity toward aqueous chlorinated phenols.

Second-order kinetic constants (k(OH,S)) for the hydroxyl free radical attack on a series of nine chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 2,5-dichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol, 2,3,5,6-tetrachlorophenol, 2,3,4,5-tetrachlorophenol, 2,3,4,6-tetrachlorophenol, and pentachlorophenol) in aqueous solution were determined by means of the competitive kinetics method. Experimental values ranged from 3.5 x 10(09)M(-1)s(-1) for pentachlorophenol to 8.2 x 10(09)M(-1)s(-1) for 2-chlorophenol. A general trend of lower kinetic constant values with higher degree of chlorination was observed and tested with four different correlations using Hammett's sigma values, the number of chlorine substituents on the aromatic ring, and estimated diffusion coefficients. These correlations were statistically significant (alpha=0.01), although the regression coefficients were moderate (R(2)<0.6). Statistical analysis indicated that all correlations were equally valid. This report includes second-order kinetic constants not previously reported for six chlorophenols, and also provides the means to estimate constants for other chlorophenols for which no experimental data are available.

Chlorine↗

PubMed2005

Comparison of protein and peptide prefractionation methods for the shotgun proteomic analysis of Synechocystis sp. PCC 6803.

Proteome analysis by gel-free "shotgun" proteomics relies on the simplification of a peptide mixture before it is analyzed in a mass spectrometer. While separation on a reverse-phase (RP) liquid chromatographic column is widely employed, a variety of other methods have been used to fractionate both proteins and peptides before this step. We compared six different protein and peptide fractionation workflows, using Synechocystis sp. PCC 6803, a useful model cyanobacterium for potential exploitation to improve its production of hydrogen and other secondary metabolites. Pre-digestion protein separation was performed by strip-based isoelectric focusing, one-dimensional polyacrylamide gel electrophoresis, or weak anion exchange chromatography, while pre-RP peptide separation was accomplished by isoelectric focusing (IEF) or strong cation exchange chromatography. Peptides were identified using electrospray ionization quadrupole time of flight-tandem mass spectrometry. Mass spectrometry (MS) and tandem mass spectra were analyzed using ProID software employing both a single organism database and the entire NCBI non-redundant database, and a total of 776 proteins were identified using a stringent set of selection criteria. Method comparisons were made on the basis of the results obtained (number and types of proteins identified), as well as ease of use and other practical aspects. IEF-IEF protein and peptide fractionation prior to RP gave the best overall performance.

Chromatography, High Pressure Liquid↗

PubMed2005

Protein engineering of epoxide hydrolase from Agrobacterium radiobacter AD1 for enhanced activity and enantioselective production of (R)-1-phenylethane-1,2-diol.

DNA shuffling and saturation mutagenesis of positions F108, L190, I219, D235, and C248 were used to generate variants of the epoxide hydrolase of Agrobacterium radiobacter AD1 (EchA) with enhanced enantioselectivity and activity for styrene oxide and enhanced activity for 1,2-epoxyhexane and epoxypropane. EchA variant I219F has more than fivefold-enhanced enantioselectivity toward racemic styrene oxide, with the enantiomeric ratio value (E value) for the production of (R)-1-phenylethane-1,2-diol increased from 17 for the wild-type enzyme to 91, as well as twofold-improved activity for the production of (R)-1-phenylethane-1,2-diol (1.96 +/- 0.09 versus 1.04 +/- 0.07 micromol/min/mg for wild-type EchA). Computer modeling indicated that this mutation significantly alters (R)-styrene oxide binding in the active site. Another three variants from EchA active-site engineering, F108L/C248I, I219L/C248I, and F108L/I219L/C248I, also exhibited improved enantioselectivity toward racemic styrene oxide in favor of production of the corresponding diol in the (R) configuration (twofold enhancement in their E values). Variant F108L/I219L/C248I also demonstrated 10-fold- and 2-fold-increased activity on 5 mM epoxypropane (24 +/- 2 versus 2.4 +/- 0.3 micromol/min/mg for the wild-type enzyme) and 5 mM 1,2-epoxyhexane (5.2 +/- 0.5 versus 2.6 +/- 0.0 micromol/min/mg for the wild-type enzyme). Both variants L190F (isolated from a DNA shuffling library) and L190Y (created from subsequent saturation mutagenesis) showed significantly enhanced activity for racemic styrene oxide hydrolysis, with 4.8-fold (8.6 +/- 0.3 versus 1.8 +/- 0.2 micromol/min/mg for the wild-type enzyme) and 2.7-fold (4.8 +/- 0.8 versus 1.8 +/- 0.2 micromol/min/mg for the wild-type enzyme) improvements, respectively. L190Y also hydrolyzed 1,2-epoxyhexane 2.5 times faster than the wild-type enzyme.

DNA Shuffling↗

PubMed2004

Active site engineering of the epoxide hydrolase from Agrobacterium radiobacter AD1 to enhance aerobic mineralization of cis-1,2-dichloroethylene in cells expressing an evolved toluene ortho-monooxygenase.

Chlorinated ethenes are the most prevalent ground-water pollutants, and the toxic epoxides generated during their aerobic biodegradation limit the extent of transformation. Hydrolysis of the toxic epoxide by epoxide hydrolases represents the major biological detoxification strategy; however, chlorinated epoxyethanes are not accepted by known bacterial epoxide hydrolases. Here, the epoxide hydrolase from Agrobacterium radiobacter AD1 (EchA), which enables growth on epichlorohydrin, was tuned to accept cis-1,2-dichloroepoxyethane as a substrate by accumulating beneficial mutations from three rounds of saturation mutagenesis at three selected active site residues, Phe-108, Ile-219, and Cys-248 (no beneficial mutations were found at position Ile-111). The EchA F108L/I219L/C248I variant coexpressed with a DNA-shuffled toluene ortho-monooxygenase, which initiates attack on the chlorinated ethene, enhanced the degradation of cis-dichloroethylene (cis-DCE) an infinite extent compared with wild-type EchA at low concentrations (6.8 microm) and up to 10-fold at high concentrations (540 microm). EchA variants with single mutations (F108L, I219F, or C248I) enhanced cis-DCE mineralization 2.5-fold (540 microm), and EchA variants with double mutations, I219L/C248I and F108L/C248I, increased cis-DCE mineralization 4- and 7-fold, respectively (540 microm). For complete degradation of cis-DCE to chloride ions, the apparent Vmax/Km for the Escherichia coli strain expressing recombinant the EchA F108L/I219L/C248I variant was increased over 5-fold as a result of the evolution of EchA. The EchA F108L/I219L/C248I variant also had enhanced activity for 1,2-epoxyhexane (2-fold) and the natural substrate epichlorohydrin (6-fold).

Agrobacterium tumefaciens↗

PubMed2004

Protein engineering of toluene ortho-monooxygenase of Burkholderia cepacia G4 for regiospecific hydroxylation of indole to form various indigoid compounds.

Previous work showed that random mutagenesis produced a mutant of toluene ortho-monooxygenase (TOM) of Burkholderia cepacia G4 containing the V106A substitution in the hydroxylase alpha-subunit (TomA3) that changed the color of the cell suspension from wild-type brown to green in rich medium. Here, DNA shuffling was used to isolate a random TOM mutant that turned blue due to mutation TomA3 A113V. To better understand the TOM reaction mechanism, we studied the specificity of indole hydroxylation using a spectrum of colored TOM mutants expressed in Escherichia coli TG1 and formed as a result of saturation mutagenesis at TomA3 positions A113 and V106. Colonies expressing these altered enzymes ranged in color from blue through green and purple to orange; and the enzyme products were identified using thin-layer chromatography, high performance liquid chromatography, and liquid chromatography-mass spectroscopy. Derived from the single TOM template, enzymes were identified that produced primarily isoindigo (wild-type TOM), indigo (A113V), indirubin (A113I), and isatin (A113H and V106A/A113G). The discovery that wild-type TOM formed isoindigo via C-2 hydroxylation of the indole pyrrole ring makes this the first oxygenase shown to form this compound. Variant TOM A113G was unable to form indigo, indirubin, or isoindigo (did not hydroxylate the indole pyrrole ring), but produced 4-hydroxyindole and unknown yellow compounds from C-4 hydroxylation of the indole benzene ring. Mutations at V106 in addition to A113G restored C-3 indole oxidation, so along with C-2 indole oxidation, isatin, indigo, and indirubin were formed. Other TomA3 V106/A113 mutants with hydrophobic, polar, or charged amino acids in place of the Val and/or Ala residues hydroxylated indole at the C-3 and C-2 positions, forming isatin, indigo, and indirubin in a variety of distributions. Hence, for the first time, a single enzyme was genetically modified to produce a wide range of colors from indole.

Base Sequence↗

PubMed2004

Metabolic pathway engineering to enhance aerobic degradation of chlorinated ethenes and to reduce their toxicity by cloning a novel glutathione S-transferase, an evolved toluene o-monooxygenase, and gamma-glutamylcysteine synthetase.

Aerobic, co-metabolic bioremediation of trichloroethylene (TCE), cis-1,2-dichloroethylene (cis-DCE) and other chlorinated ethenes with monooxygenase-expressing microorganisms is limited by the toxic epoxides produced as intermediates. A recombinant Escherichia coli strain less sensitive to the toxic effects of cis-DCE, TCE and trans-1,2-dichloroethylene (trans-DCE) degradation has been created by engineering a novel pathway consisting of eight genes including a DNA-shuffled toluene ortho-monooxygenase from Burkholderia cepacia G4 (TOM-Green), a newly discovered glutathione S-transferase (GST) from RhodococcusAD45 (IsoILR1), found to have activity towards epoxypropane and cis-DCE epoxide, and an overexpressed E. coli mutant gamma-glutamylcysteine synthetase (GSHI*). Along with IsoILR1, another new RhodococcusAD45 GST, IsoILR2, was cloned that lacks activity towards cis-DCE epoxide and differs from IsoILR1 by nine amino acids. The recombinant strain in which TOM-Green and IsoILR1 were co-expressed on separate plasmids degraded 1.9-fold more cis-DCE compared with a strain that lacked IsoILR1. In the presence of IsoILR1 and TOM-Green, the addition of GSH1* resulted in a sevenfold increase in the intracellular GSH concentration and a 3.5-fold improvement in the cis-DCE degradation rate based on chloride released (2.1 +/- 0.1 versus 0.6 +/- 0.1 nmol min(-1) mg(-1) protein at 540 microM), a 1.8-fold improvement in the trans-DCE degradation rate (1.29 +/- 0.03 versus 0.71 +/- 0.04 nmol x min(-1) mg(-1) protein at 345 microM) and a 1.7-fold improvement in the TCE degradation rate (6.8 +/- 0.24 versus 4.1 +/- 0.16 nmol x min(-1) mg(-1) protein at 339 microM). For cis-DCE degradation with TOM-Green (based on substrate depletion), V(max) was 27 nmol x min(-1) mg(-1) protein with both IsoILR1 and GSHI* expressed compared with V(max) = 10 nmol x min(-1) mg(-1) protein for the GST(-)GSHI*(-) strain. In addition, cells expressing IsoILR1 and GSHI* grew 78% faster in rich medium than a strain lacking these two heterologous genes.

Amino Acid Sequence↗

PubMed2004

Saturation mutagenesis of toluene ortho-monooxygenase of Burkholderia cepacia G4 for Enhanced 1-naphthol synthesis and chloroform degradation.

Directed evolution of toluene ortho-monooxygenase (TOM) of Burkholderia cepacia G4 previously created the hydroxylase alpha-subunit (TomA3) V106A variant (TOM-Green) with increased activity for both trichloroethylene degradation (twofold enhancement) and naphthalene oxidation (six-times-higher activity). In the present study, saturation mutagenesis was performed at position A106 with Escherichia coli TG1/pBS(Kan)TOMV106A to improve TOM activity for both chloroform degradation and naphthalene oxidation. Whole cells expressing the A106E variant had two times better naphthalene-to-1-naphthol activity than the wild-type cells (V(max) of 9.3 versus 4.5 nmol.min(-1).mg of protein(-1) and unchanged K(m)), and the regiospecificity of the A106E variant was unchanged, with 98% 1-naphthol formed, as was confirmed with high-pressure liquid chromatography. The A106E variant degrades its natural substrate toluene 63% faster than wild-type TOM does (2.12 +/- 0.07 versus 1.30 +/- 0.06 nmol.min(-1).mg of protein(-1) [mean +/- standard deviation]) at 91 microM and has a substantial decrease in regiospecificity, since o-cresol (50%), m-cresol (25%), and p-cresol (25%) are formed, in contrast to the 98% o-cresol formed by wild-type TOM. The A106E variant also has an elevated expression level compared to that of wild-type TOM, as evidenced by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Another variant, the A106F variant, has 2.8-times-better chloroform degradation activity based on gas chromatography (V(max) of 2.61 versus 0.95 nmol.min(-1).mg of protein(-1) and unchanged K(m)) and chloride release (0.034 +/- 0.002 versus 0.012 +/- 0.001 nmol.min(-1).mg of protein(-1)). The A106F variant also was expressed at levels similar to those of wild-type TOM and 62%-better toluene oxidation activity than wild-type TOM (2.11 +/- 0.3 versus 1.30 +/- 0.06 nmol.min(-1).mg of protein(-1)). A shift in regiospecificity of toluene hydroxylation was also observed for the A106F variant, with o-cresol (28%), m-cresol (18%), and p-cresol (54%) being formed. Statistical analysis was used to estimate that 292 colonies must be screened for a 99% probability that all 64 codons were sampled during saturation mutagenesis.

Binding Sites↗

PubMed2003

Proteomic changes in Escherichia coli TG1 after metabolic engineering for enhanced trichloroethene biodegradation.

Through metabolic engineering, new enzymatic pathways can be introduced into cells to enable or enhance production or biotransformation of chemicals. However, these changes have physiological consequences that can be important but are not well understood. Here we describe the use of two-dimensional gel electrophoresis (2-DE) to detect changes in the proteome of Escherichia coli cells that have been engineered to transform the pollutant trichloroethene (TCE) with the enzyme toluene o-monooxygenase (TOM). Comparison of 2-DE gels (isoelectric point range 4-7) for E. coli cells with and without the ability to synthesize TOM revealed 31 new proteins in TOM-containing cells as well as nine proteins not detected in those cells but present in the plasmid control strain. Exposure of TOM-containing cells to TCE led to the synthesis of four new proteins and the loss of only one protein. Thus, this example of metabolic engineering has a substantial and complex impact on the physiology of these cells that was clearly revealed using a proteomic approach.

Bacterial Proteins↗

PubMed2002

Jay Bailey as mentor--the students' perspective.

Professor James E. Bailey was not only a world-renowned leader and pioneer in biochemical engineering but also a mentor to the many graduate students and postdoctoral researchers in his group. To provide non-"Bailey-ites" with an impression of Jay as a mentor, we begin with a brief review of his career, focusing on the dynamics of the research group. Typical student experiences of being part of the Bailey group are then discussed, including the recognition of a particular research style and Jay's expectations for hard work. Finally, we provide some thoughts on Jay's mentoring style, which was marked by an ability to foster independence, a sense of quality, and passion for research. Jay's contributions as a mentor can perhaps be recognized as being as significant as his research achievements.

Biochemistry↗

PubMed2002

Two-dimensional electrophoresis analysis of protein production during growth of Pseudomonas putida F1 on toluene, phenol, and their mixture.

The protein profiles of Pseudomonas putida F1 during growth on toluene, phenol, and their mixture were examined by two-dimensional polyacrylamide gel electrophoresis. Although this bacterium uses the same catabolic pathway for both substrates, P. putida F1 produced specific sets of proteins in response to toluene and phenol as single or mixed substrates. Proteins associated with growth on these substrates could be classified into three categories: ten Group T proteins were associated with the degradation of toluene, seventeen Group P proteins were associated with the degradation of phenol, and one Group M protein was observed to be associated only with toluene-phenol mixture degradation. During growth on the mixture, the protein profile of the cells shifted from Group T proteins to Group P proteins. This correlated well with the substrate consumption pattern, in which toluene was consumed first and growth on phenol did not begin until the medium was nearly depleted of toluene. Individual Group T and Group P protein intracellular concentrations had different transients as the cells grew on the mixture; seven protein levels increased, four decreased, and sixteen reached a maximum and then declined. The Group M protein reached a concentration maximum near the time when growth on phenol began. Variations in the maintenance of these proteins were also noted. These results demonstrate that cells growing on a mixture of substrates undergo significant physiological changes. Further investigation of these changes is expected to shed light on the unusual biodegradation kinetics previously observed with this mixed-substrate system.

Bacterial Proteins↗

PubMed2002

Biodegradation kinetics of aromatic hydrocarbon mixtures by pure and mixed bacterial cultures.

Microbial growth on pollutant mixtures is an important aspect of bioremediation and wastewater treatment. However, efforts to develop mathematical models for mixed substrate kinetics have been limited. Nearly all models group either the microbial population (as "biomass") or the chemical species (e.g., as biological oxygen demand). When individual chemical species are considered, most models assume either no interaction or that the nature of the interaction is competition for the same rate-limiting enzyme. And when individual microbial species are considered, simple competition for the growth substrate is the only interaction included. Here, we present results using Pseudomonas putida F1 and Burkholderia sp. strain JS150 growing individually and together on benzene, toluene, phenol, and their mixtures and compare mathematical models to describe these results. We demonstrate that the simple models do not accurately predict the outcome of these biodegradation experiments, and we describe the development of a new model for substrate mixtures, the sum kinetics with interaction parameters (SKIP) model. In mixed-culture experiments, the interactions between species were substrate dependent and could not be predicted by simple competition models. Together, this set of experimental and modeling results presents our current state of work in this area and identifies challenges for future modeling efforts.

Biodegradation, Environmental↗

PubMed2002

Application of biologically based computer modeling to simple or complex mixtures.

The complexity and the astronomic number of possible chemical mixtures preclude any systematic experimental assessment of toxicology of all potentially troublesome chemical mixtures. Thus, the use of computer modeling and mechanistic toxicology for the development of a predictive tool is a promising approach to deal with chemical mixtures. In the past 15 years or so, physiologically based pharmacokinetic/pharmacodynamic (PBPK/PD) modeling has been applied to the toxicologic interactions of chemical mixtures. This approach is promising for relatively simple chemical mixtures; the most complicated chemical mixtures studied so far using this approach contained five or fewer component chemicals. In this presentation we provide some examples of the utility of PBPK/PD modeling for toxicologic interactions in chemical mixtures. The probability of developing predictive tools for simple mixtures using PBPK/PD modeling is high. Unfortunately, relatively few attempts have been made to develop paradigms to consider the risks posed by very complex chemical mixtures such as gasoline, diesel, tobacco smoke, etc. However, recent collaboration between scientists at Colorado State University and engineers at Rutgers University attempting to use reaction network modeling has created hope for the possible development of a modeling approach with the potential of predicting the outcome of toxicology of complex chemical mixtures. We discuss the applications of reaction network modeling in the context of petroleum refining and its potential for elucidating toxic interactions with mixtures.

Computer Simulation↗