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Susan C. Roberts - One of the best experts on this subject based on the ideXlab platform.
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Analysis of Aggregate Size as a process variable affecting paclitaxel accumulation in Taxus suspension cultures.
Biotechnology progress, 2011Co-Authors: Martin E. Kolewe, Michael A. Henson, Susan C. RobertsAbstract:Plant cell Aggregates have long been implicated in affecting cellular metabolism in suspension culture, yet the rigorous characterization of Aggregate Size as a process variable and its effect on bioprocess performance has not been demonstrated. Aggregate fractionation and analysis of biomass-associated product is commonly used to assess the effect of aggregation, but we establish that this method is flawed under certain conditions and does not necessarily agree with comprehensive studies of total culture performance. Leveraging recent advances to routinely measure Aggregate Size distributions, we developed a simple method to manipulate Aggregate Size and evaluate its effect on the culture as a whole, and found that Taxus suspension cultures with smaller Aggregates produced significantly more paclitaxel than cultures with larger Aggregates in two cell lines over a range of Aggregate Sizes, and where biomass accumulation was equivalent before elicitation with methyl jasmonate. Taxus cuspidata (T. cuspidata) P93AF cultures with mean Aggregate Sizes of 690 and 1,100 μm produced 22 and 11 mg/L paclitaxel, respectively, a twofold increase for smaller Aggregates, and T. cuspidata P991 cultures with mean Aggregate Sizes of 400 and 840 μm produced 6 and 0.3 mg/L paclitaxel, respectively, an increase of 20-fold for smaller Aggregates. These results demonstrate the importance of validating experiments aimed at a specific phenomenon with total process studies, and provide a basis for treating Aggregate Size as a targeted process variable for rational control strategies.
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Characterization of Aggregate Size in Taxus suspension cell culture
Plant Cell Reports, 2010Co-Authors: Martin E. Kolewe, Michael A. Henson, Susan C. RobertsAbstract:Plant cells grow as Aggregates in suspension culture, but little is known about the dynamics of aggregation, and no routine methodology exists to measure Aggregate Size. In this study, we evaluate several different methods to characterize Aggregate Size in Taxus suspension cultures, in which Aggregate diameters range from 50 to 2,000 μm, including filtration and image analysis, and develop a novel method using a specially equipped Coulter counter system. We demonstrate the suitability of this technology to measure plant cell culture Aggregates, and show that it can be reliably used to measure total biomass accumulation compared to standard methods such as dry weight. Furthermore, we demonstrate that all three methods can be used to measure an Aggregate Size distribution, but that the Coulter counter is more reliable and much faster, and also provides far better resolution. While absolute measurements of Aggregate Size differ based on the three evaluation techniques, we show that linear correlations are sufficient to account for these differences ( R ^2 > 0.99). We then demonstrate the utility of the novel Coulter counter methodology by monitoring the dynamics of a batch process and find that the mean Aggregate Size increases by 55% during the exponential growth phase, but decreases during stationary phase. The results indicate that the Coulter counter method can be routinely used for advanced process characterization, particularly to study the relationship between Aggregate Size and secondary metabolite production, as well as a source of reliable experimental data for modeling aggregation dynamics in plant cell culture.
Saskia Keesstra - One of the best experts on this subject based on the ideXlab platform.
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Interrill erodibility in relation to Aggregate Size class in a semi-arid soil under simulated rainfalls
CATENA, 2018Co-Authors: Ali Reza Vaezi, Seyedeh Fatemeh Eslami, Saskia KeesstraAbstract:Abstract Interrill erodibility can be affected by soil Aggregates, especially by those Aggregate Size classes that are dominant in the soil. In the Water erosion Prediction Project (WEPP) model, interrill soil erodibility (Ki) is estimated using very fine sand content. Despite that some studies have indicated an effect of Aggregate stability on the Ki, information on the relationship between the Aggregate Size class and Ki and factors controlling it, particularly in semi-arid region is limited. This study was conducted to determine the variation of Ki for different Aggregate Size classes under various rainfall intensities and evaluation of the WEPP model in estimating the Ki for different Aggregate fractions. Five Aggregate Size classes (0.25–2, 2–4.75, 4.75–5.6, 5.6–9.75 mm, and 9.75–12.7 mm) were separated from a sandy clay loam soil sampled in an agricultural land and put in laboratory flumes of 100 cm × 50 cm. The flumes were placed on a 9% slope and exposed to ten sequential rainfall simulations varying from 10 to 60 mm h−1 for 30 min. The Ki of each Aggregate Size classes was determined using the interrill sediment delivery rate and compared this with the values estimated using WEPP. All physicochemical properties were also determined in the Aggregate Size classes. Organic matter content in the Aggregate Size classes was very low (0.65–0.73%) and didn't show strong relationships with the Aggregate stability and hydraulic conductivity, whereas clay was major factor controlling determining these properties for the different Aggregate fractions. Significant differences were found among the Aggregate Size classes in clay content (P
C. E. Pallud - One of the best experts on this subject based on the ideXlab platform.
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Modeling the impact of soil Aggregate Size on selenium immobilization
Biogeosciences, 2013Co-Authors: M. F. Kausch, C. E. PalludAbstract:Soil Aggregates are mm- to cm-Sized microporous structures separated by macropores. Whereas fast advective transport prevails in macropores, advection is inhibited by the low permeability of intra-Aggregate micropores. This can lead to mass transfer limitations and the formation of Aggregate scale concentration gradients affecting the distribution and transport of redox sensitive elements. Selenium (Se) mobilized through irrigation of seleniferous soils has emerged as a major aquatic contaminant. In the absence of oxygen, the bioavailable oxyanions selenate, Se(VI), and selenite, Se(IV), can be microbially reduced to solid, elemental Se, Se(0), and anoxic microzones within soil Aggregates are thought to promote this process in otherwise well-aerated soils. To evaluate the impact of soil Aggregate Size on selenium retention, we developed a dynamic 2-D reactive transport model of selenium cycling in a single idealized Aggregate surrounded by a macropore. The model was developed based on flow-through-reactor experiments involving artificial soil Aggregates (diameter: 2.5 cm) made of sand and containing Enterobacter cloacae SLD1a-1 that reduces Se(VI) via Se(IV) to Se(0). Aggregates were surrounded by a constant flow providing Se(VI) and pyruvate under oxic or anoxic conditions. In the model, reactions were implemented with double-Monod rate equations coupled to the transport of pyruvate, O 2 , and Se species. The spatial and temporal dynamics of the model were validated with data from experiments, and predictive simulations were performed covering Aggregate Sizes 1–2.5 cm in diameter. Simulations predict that selenium retention scales with Aggregate Size. Depending on O 2 , Se(VI), and pyruvate concentrations, selenium retention was 4–23 times higher in 2.5 cm Aggregates compared to 1 cm Aggregates. Under oxic conditions, Aggregate Size and pyruvate concentrations were found to have a positive synergistic effect on selenium retention. Promoting soil aggregation on seleniferous agricultural soils, through organic matter amendments and conservation tillage, may thus help decrease the impacts of selenium contaminated drainage water on downstream aquatic ecosystems.
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Modeling the impact of soil Aggregate Size on selenium immobilization
2012Co-Authors: M. F. Kausch, C. E. PalludAbstract:Abstract. Soil Aggregates are mm- to cm-Sized microporous structures separated by macropores. Whereas fast advective transport prevails in macropores, advection is inhibited by the low permeability of intra-Aggregate micropores. This can lead to mass transfer limitations and the formation of Aggregate-scale concentration gradients affecting the distribution and transport of redox sensitive elements. Selenium (Se) mobilized through irrigation of seleniferous soils has emerged as a major aquatic contaminant. In the absence of oxygen, the bioavailable oxyanions selenate, Se(VI), and selenite, Se(IV), can be microbially reduced to solid, elemental Se, Se(0), and anoxic microzones within soil Aggregates are thought to promote this process in otherwise well aerated soils. To evaluate the impact of soil Aggregate Size on selenium retention, we developed a dynamic 2-D reactive transport model of selenium cycling in a single idealized Aggregate surrounded by a macropore. The model was developed based on flow-through-reactor experiments involving artificial soil Aggregates (diameter: 2.5 cm) made of sand and containing Enterobacter cloacae SLD1a-1 that reduces Se(VI) via Se(IV) to Se(0). Aggregates were surrounded by a constant flow providing Se(VI) and pyruvate under oxic or anoxic conditions. In the model, reactions were implemented with double-Monod rate equations coupled to the transport of pyruvate, O2, and Se-species. The spatial and temporal dynamics of the model were validated with data from experiments and predictive simulations were performed covering Aggregate Sizes between 1 and 2.5 cm diameter. Simulations predict that selenium retention scales with Aggregate Size. Depending on O2, Se(VI), and pyruvate concentrations, selenium retention was 4–23 times higher in 2.5-cm-Aggregates compared to 1-cm-Aggregates. Under oxic conditions, Aggregate Size and pyruvate-concentrations were found to have a positive synergistic effect on selenium retention. Promoting soil aggregation on seleniferous agricultural soils, through organic matter amendments and conservation tillage, may thus help decrease the impacts of selenium contaminated drainage water on downstream aquatic ecosystems.
Douglas L. Karlen - One of the best experts on this subject based on the ideXlab platform.
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Influence of soil Aggregate Size on atrazine sorption kinetics
Journal of Agricultural and Food Chemistry, 1994Co-Authors: Jeffrey M. Novak, T. B. Moorman, Douglas L. KarlenAbstract:Soil Aggregate Size may be an important physical property regulating herbicide behavior; however, little information exists to evaluate this effect. The influence of Aggregate Size on atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] sorption coefficients (K d ) and sorption kinetics is investigated by batch equilibration using a suite of whole (0-5 mm) and crushed (
Jeffrey M. Novak - One of the best experts on this subject based on the ideXlab platform.
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Water Treatment Residuals Aggregate Size Influences Phosphorus Sorption Kinetics And Pmax Values
Soil Science, 2005Co-Authors: Jeffrey M. Novak, Donald W. WattsAbstract:Drinking water treatment residuals (WTRs) are used as a soil amendment to minimize off-site P movement and increase a soil's phosphorus (P) sorption capacity. The Aggregate Size of WTRs may affect sorption kinetics and P sorption maxima (P max ) values. We hypotheSize that finer-Sized WTRs Aggregates will have higher kinetic sorption rates and P max values than coarser-Size Aggregates. The objectives were to determine WTRs Aggregate Size effects on kinetic rates of P sorption, on the magnitude of P max values, and the time necessary to reach equilibrium with P. A WTR sample was ground and sieved into five Aggregate Size ranges ( 4 mm). Phosphorus sorption isotherms for each Aggregate Size range were determined as a function of time (between 24 and 120 h). Reaction rate constants (k) were determined by using a first-order reaction equation and P max values for each Aggregate Size range were calculated from the linear form of the Langmuir equation. The 4.0-mm) had P max values of 98 mg g -1 . Aggregate Size has an important influence on WTRs P sorption characteristics; therefore, it is recommended that Aggregate Size should be strongly considered when determining P isotherms or using residuals as a soil amendment to reduce non-point source P contamination of surface water bodies.
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Influence of soil Aggregate Size on atrazine sorption kinetics
Journal of Agricultural and Food Chemistry, 1994Co-Authors: Jeffrey M. Novak, T. B. Moorman, Douglas L. KarlenAbstract:Soil Aggregate Size may be an important physical property regulating herbicide behavior; however, little information exists to evaluate this effect. The influence of Aggregate Size on atrazine [6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine] sorption coefficients (K d ) and sorption kinetics is investigated by batch equilibration using a suite of whole (0-5 mm) and crushed (
