Rodney S. Skeen

Pacific Northwest National Laboratory, Richland, Washington, United States

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Publications (49)113 Total impact

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    ABSTRACT: Data are presented that demonstrate a batch reactor that allows accurate monitoring of process dynamics during biodegradation of volatile organics. Using this system, many samples can be removed in a aseptic fashion, allowing frequent measurements of the concentrations of biomass, electron donors, electron acceptors, and volatile compounds. Additionally, the reactor is well instrumented, allowing the continuous monitoring of pH, oxidation/reduction potential, pressure, and temperature. The reactor is constructed entirely of materials which have minimal interaction with volatile organic compounds. It is also demonstrated that sample removal does not cause losses of volatile compounds since the sampling ports are double sealed, making use of both gastight stainless steel ball valves and Teflon-lined septa.
    Environmental Progress 07/2006; 13(3):174 - 177. · 0.92 Impact Factor
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    ABSTRACT: A denitrifying consortium capable of transforming carbon tetrachloride (CCl4) was cultured from aquifer sediment from the U.S. Department of Energy's Hanford Site in southeastern Washington State. To understand the kinetics of the biological destruction of CCl4 by these microbes, a set of experiments, the conditions of which were chosen according to a fractional factorial experimental design, were completed. This article reports on the experimental design along with the results for CCl4, biomass, acetate, nitrate, and nitrite concentrations. These data indicate that growth is inhibited by high nitrite concentrations, whereas CCl4 degradation is slowed by the presence of nitrate and/or nitrite. © 1994 John Wiley & Sons, Inc.
    Biotechnology and Bioengineering 02/2004; 43(6):521 - 528. · 4.16 Impact Factor
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    ABSTRACT: A denitrifying consortium capable of transforming carbon tetrachloride (CCI4) was cultured from an aquifer soil sample from the U.S. Department of Energy's Hanford Site in southeastern Washington State. A mathematical description of the kinetics of CCI4 destruction by this microbial consortium is presented, and its prediction are compared to experimental data. The model successfully predicted the concentrations of acetate, nitrate, nitrite, biomass, and CCI4 for all 12 experiments (a total of 60 concentration-vs.-time data sets). In addition, no statistically significant interactions exist between parameter values and individual test conditions. The ability of the model to predict the results of a treatability test for CCI4 degradation in Hanford groundwater, without adjusting any model parameters, is discussed. © 1994 John Wiley & Sons, Inc.
    Biotechnology and Bioengineering 02/2004; 44(2):211 - 218. · 4.16 Impact Factor
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    ABSTRACT: The present invention provides the promoter clone discovery of an alpha-amylase gene of a starch utilizing yeast strain Schwanniomyces castellii. The isolated alpha-amylase promoter is an inducible promoter, which can regulate strong gene expression in starch culture medium.
    01/2003;
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    ABSTRACT: The present invention provides the promoter clone discovery of an alpha-amylase gene of a starch utilizing yeast strain Schwanniomyces castellii. The isolated alpha-amylase promoter is an inducible promoter, which can regulate strong gene expression in starch culture medium.
    01/2003;
  • Johnway Gao, Rodney S. Skeen
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    ABSTRACT: The present invention provides the promoter clone discovery of phosphoglycerate kinase gene 2 of a lactic acid-producing filamentous fungal strain, Rhizopus oryzae. The isolated promoter can constitutively regulate gene expression under various carbohydrate conditions. In addition, the present invention also provides a design of an integration vector for the transformation of a foreign gene in Rhizopus oryzae.
    Year: 12/2002
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    ABSTRACT: A flexible system was developed for the simultaneous conversion of biomass to industrial chemicals and the production of industrial biocatalysts. In particular, the expression of a bacterial enzyme, beta-glucuronidase (GUS), was investigated using a genetically modified starch-degrading Saccharomyces strain in suspension cultures in starch media. Different sources of starch including corn and waste potato starch were used for yeast biomass accumulation and GUS expression studies under controls of inducible and constitutive promoters. A thermostable bacterial cellulase, Acidothermus cellulolyticus E1 endoglucanase gene was also cloned into an episomal plasmid expression vector and expressed in the starch-degrading Saccharomyces strain.
    01/2002;
  • Jianwei Gao, Rodney S Skeen
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    ABSTRACT: The capability of the simple carbohydrate, glucose, to stimulate aerobic biodegradation of cis-dichloroethylene (cis-DCE) was tested using a river sediment. Greater reductions in cis-DCE were observed in aerobic microcosms incubated with glucose than in either killed controls, bottles incubated with oxygen and no glucose, or bottles containing glucose and no oxygen. Two aquifer sediments from different geographic locations also showed similar trends in dichloroethylene reduction. A sediment-free transfer culture from the original river sediment was further tested for cis-DCE degradation. Results indicate that cis-DCE losses coincide with an increase in chloride-ion concentration. The increase was equivalent to the amount of chloride that would be expected from the measured reduction in dichloroethylene and the release of two chlorides per cis-DCE. The possibility that methanotrophic or ammonia-oxidizing bacteria mediated dichloroethylene destruction was eliminated, because the sediment-free suspension culture showed no evidence of either activity. Hence, it appears that a new type of activity mediated the observed dichloroethylene transformation. The implications of these results on in situ bioremediation of chloroethylenes are discussed.
    Water Research 08/1999; · 4.66 Impact Factor
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    ABSTRACT: Fed-batch experiments were performed to determine the carbon tetrachloride (CT)-degrading ability of three denitrifying consortia cultured from sites not contaminated with CT. A mathematical model was used to quantify the rates of CT transformation by the consortia under both acetate-limiting and nitrate-limiting conditions. A rate constant for CT transformation on a cellular protein basis and the fraction of degraded CT transformed to chloroform (CF) were determined for each consortium by optimizing the model to fit the experimental data. The parameters for these experiments were statistically compared to those obtained for previous experiments with a denitrifying consortium cultured from an aquifer soil sample from the US Department of Energy Hanford site in southeastern Washington state. Results of F-test analysis indicated the rate of CT transformation and the production of CF both were functions of the limiting nutrient. Under nitrate-limited conditions, the rate constant for CT transformation for all four consortia was about 30 L/gmol/min and approximately 50% of the CT transformed was converted to CF. When acetate was the limiting nutrient, the rate constant for CT transformation was approximately 8 L/gmol/min and the CF yield decreased to about 25%. These results imply the ability to degrade CT may be inherent to some denitrifying organisms, regardless of previous exposure to CT. Copyright 1999 John Wiley & Sons, Inc.
    Biotechnology and Bioengineering 08/1999; 64(3):342-8. · 4.16 Impact Factor
  • B S Hooker, R S Skeen
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    ABSTRACT: The EPA National Priority List contains 22 ammunition production and processing sites that are laden with explosive and propellant wastes. With levels of 2,4,6-trinitrotoluene (TNT) contamination as high as 200 g/kg of solids, some of these sites are literally on the verge of exploding. They also present serious exposure risks to humans and wildlife, as many of these contaminants are also strong toxins and mutagens. In this issue, French et al. describe a new option for cleaning up this dangerous mixture: the use of transgenic plants. They engineered plants to express a bacterial enzyme that can completely denitrify TNT and trinitroglycerin (GTN) into harmless compounds.
    Nature Biotechnology 06/1999; 17(5):428. · 32.44 Impact Factor
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    ABSTRACT: A direct method for transforming multiple solute transport equations, coupled by linear, series, and/or parallel first-order, irreversible reactions, into a series of simple transport equations having known solutions is developed. Using this method, previously published analytical solutions to single-species transport problems, in which the transported species reacts with first-order kinetics, can be used to derive analytical solutions to multispecies transport systems with parallel, serial, and combined reaction networks. This new method overcomes many of the limitations that were implicit in previously published methods. In particular, the number of species that can be described is unlimited, and the reaction stoichiometry does not have to be unimolar. To illustrate the method, an analytical solution is derived for a five-species serial-parallel reactive transport system. The analytical solution obtained for this problem is compared with a numerical solution obtained with a previously developed code. This analytical method is applicable to the verification of new numerical codes.
    Water Resources Research 01/1999; 35(1):185-190. · 3.15 Impact Factor
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    ABSTRACT: A denitrifying consortium capable of degrading carbon tetrachloride (CT) was shown to also degrade 1,1,1-trichloroethane (TCA). Fed-batch experiments demonstrated that the specific rate of TCA degradation by the consortium was comparable to the specific rate of CT degradation (approximately 0.01 L/gmol/min) and was independent of the limiting nutrient. Although previous work demonstrated that 4-50% of CT transformed by the consortium was converted to chloroform (CF), no reductive dechlorination products were detected during TCA degradation, regardless of the limiting nutrient. The lack of chlorinated TCA degradation products implies that the denitrifying consortium possesses an alternate pathway for the degradation of chlorinated solvents which does not involve reductive dechlorination. Copyright 1998 John Wiley & Sons, Inc.
    Biotechnology and Bioengineering 09/1998; 59(4):393-9. · 4.16 Impact Factor
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    ABSTRACT: A denitrifying consortium capable of degrading carbon tetrachloride (CT) was shown to also degrade 1,1,1-trichloroethane (TCA). Fed-batch experiments demonstrated that the specific rate of TCA degradation by the consortium was comparable to the specific rate of CT degradation (approximately 0.01 L/gmol/min) and was independent of the limiting nutrient. Although previous work demonstrated that 4–50% of CT transformed by the consortium was converted to chloroform (CF), no reductive dechlorination products were detected during TCA degradation, regardless of the limiting nutrient. The lack of chlorinated TCA degradation products implies that the denitrifying consortium possesses an alternate pathway for the degradation of chlorinated solvents which does not involve reductive dechlorination. © 1998 John Wiley & Sons, Inc. Biotechnol Bioeng 59:393–399, 1998.
    Biotechnology and Bioengineering 08/1998; 59(4). · 4.16 Impact Factor
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    ABSTRACT: Due to industrial, agricultural, and defense operations, chlorinated solvents, and their natural transformation products, have been found in drinking water, wastewater, and ground water throughout the industrialized world [1]. Further, such compounds represent the most prevalent organic groundwater contaminants in the U.S. [2]. Because many are priority pollutants and/or suspected carcinogens or mutagens, the movement, transformation, and fate of these contaminants in the environment is of interest [3]. For these compounds, in situ bioremediation has the potential to substantially reduce cleanup duration and cost, when compared with traditional pump-and-treat technologies [4].
    Environmental Progress 05/1998; 17(2):104 - 110. · 0.92 Impact Factor
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    ABSTRACT: Results of a 7-month field test of in situ bioremediation of carbon tetrachloride (CT) under denitrifying conditions are reported. The demonstration was conducted in a portion of a several-square-mile CT and nitrate plume. Pretest CT and nitrate levels were 12.5 ± 0.14 μM and 3.87 ± 0.26 mM, respectively. During the test, the CT concentration dropped by 3.71 ± μM, representing an estimated total of 1.42 kg of CT destroyed. The total quantities of acetate and nitrate injected during the demonstration were 221 and 300 kg, respectively. Nitra injection was composed of short-duration, high-concentration pulses added with acetate pulses, and continuously injected nitrate that was present in the surrounding groundwater. Biomass was distributed successfully within the flow field without fouling the injection well. Levels of planktonic denitrifiers increased 10- and 5-fold in monitoring wells 3 and 6 m downstream from the injection well, respectively. A distributed growth pattern was indicated through reductions in the concentrations of acetate, nitrate, and nitrite between these wells. Chloroform (CF) production was controlled by adjusting acetate and nitrate pulsing to keep low levels of nitrate in most of the flow field. Under this regime only 1 mol% of transformed CT appeared as CF. In contrast, approximately 33 mol% of CT transformed to appear as CF when nutrient-feeding conditions were adjusted so that nitrate was consistently absent.
    Bioremediation Journal 03/1998; 1(3):181-193. · 0.40 Impact Factor
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    ABSTRACT: Anaerobic microcosms of subsurface soils from three location were used to investigate the separate effects of several electron donors on tetrachloroethylene (PCE) dechlorination activity. The substrates tested were methanol, lactate, acetate and sucrose. Various levels of sulfate-reducing, acetogenic, fermentative, and methanogenic activity were observed in all sediments. PCE dechlorination was detected in all microcosms, but the amount of dehalogenation varied by several orders of magnitude. Trichloroethylene as the primary dehalogenation product; however, small amounts of cis-1,2-dichloroethylene, 1,1-dichloroethylene, and vinyl chloride were also detected in several microcosms. Lactate-amended microcosms showed large amounts of dehalogenation in two of the three sediments. One of the two sediments which showed positive activity with lactate also had large amounts of dehalogenation with methanol. Amendment with formate, acetate, or sucrose resulted in only slight dehalogenation in the three sediments. Elevated levels of dehalogenation were not consistently associated with any observable anaerobic metabolisms (sulfate reduction, acetogenesis, fermentation, or methanogensis).
    Water Research 10/1997; · 4.66 Impact Factor
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    ABSTRACT: Soil column experiments were conducted to study bacterial growth and transport in porous media under denitrifying conditions. The study used a denitrifying microbial consortium isolated from aquifer sediments sampled at the U.S. Department of Energy's Hanford site. One-dimensional, packed-column transport studies were conducted under two substrate loading conditions. A detailed numerical model was developed to predict the measured effluent cell and substrate concentration profiles. First-order attachment and detachment models described the interphase exchange processes between suspended and attached biomass. Insignificantly different detachment coefficient values of 0.32 and 0.43 day−1, respectively, were estimated for the high and low nitrate loading conditions (48 and 5 mg l−1 NO3, respectively). Comparison of these values with those calculated from published data for aerobically growing organisms shows that the denitrifying consortium had lower detachment rate coefficients. This suggests that, similar to detachment rates in reactor-grown biofilms, detachment in porous media may increase with microbial growth rate. However, available literature data are not sufficient to confirm a specific analytical model for predicting this growth dependence.
    Journal of Contaminant Hydrology 01/1997; · 2.89 Impact Factor
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    ABSTRACT: When injecting nutrients during active bioremediation, various nutrient addition strategies can be employed in order to remediate the site at minimal expense. In particular, if more than one nutrient is required, a pulse addition strategy can be devised in which these nutrients are added as temporally separated pulses such that the biostimulated portion of the flow field can be maximized. In this manuscript, results of numerical simulations are reported which demonstrate this effect. Previously published kinetic expressions describing microbial growth and carbon tetrachloride degradation under denitrifying conditions are used in these simulations. The simulations indicate that volumetric treatment can be accomplished by injecting long duration nutrient pulses of different nutrients that are separated by a long period where only unamended water is injected. This strategy will cause the nutrient pulses to overlap at a considerable distance from the injection point, while maintaining concentrations that are high enough to ensure significant biomass growth and contaminant destruction.
    Computational Geosciences 01/1997; 1. · 1.42 Impact Factor
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    ABSTRACT: The effects of perchloroethylene (PCE) concentration in the range of 0-100 mg/L on methane and acetate production by a methanol-enriched methanogenic consortia were investigated at 17{degrees}C. The results indicate that PCE is more inhibitory to methanogenesis than to acetogenesis. At concentrations as low as 10 ppm, PCE affects the methanogenic activity of the consortium, and has completely inhibited this activity at 100 ppm. Conversely, PCE does not begin to inhibit acetogenic activity until the concentration is above 10 ppm, and has not completely inhibited it even at a PCE concentration of 100 ppm. 15 refs., 3 figs.
    Applied Biochemistry and Biotechnology 12/1996; 57-58. · 1.89 Impact Factor
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    ABSTRACT: Fed batch experiments were performed to test the effects of electron donor and electron acceptor availability on the production of chloroform (CF) during carbon tetrachloride (CT) destruction by a denitrifying bacterial consortium. In one series of tests, acetate (electron donor) was present in excess while nitrate and nitrite (electron acceptor) were limiting. In the other series of tests, acetate was the limiting nutrient, and nitrate and nitrite were in excess. Under nitrate limiting conditions, 50% (+/-17%) of the CT transformed by the microorganisms was converted to CF. However, under acetate limiting conditions, only 4% (+/-4%) of the CT that was degraded appeared as CF. Previous research had suggested that denitrifying bacteria can degrade CT via two competing pathways. One of these pathways produces CF as the predominant end product. The second pathway produces CO(2) as the primary end product. The results shown here suggest that the first pathway is dominant when nitrate and nitrite are depleted while the second pathway, which produces little CF, dominates when nitrate or nitrite are available.
    Biotechnology and Bioengineering 09/1996; 51(5):551-7. · 4.16 Impact Factor