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Ruffmann C, Calboli FCF, Bravi I, Gveric D, Curry LK, de Smith A, Pavlou S, Buxton JL, Blakemore AIF, Takousis P, Molloy S, Piccini P, Dexter DT, Roncaroli F, Gentleman SM, Middleton LT. Cortical Lewy bodies and Aβ burden are associated with prevalence and timing of dementia in Lewy body diseases. Neuropathol Appl Neurobiol 2015; 42:436-50. [DOI: 10.1111/nan.12294] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Revised: 09/24/2015] [Accepted: 11/03/2015] [Indexed: 01/16/2023]
Affiliation(s)
- C. Ruffmann
- Neuroepidemiology and Ageing Research Unit; School of Public Health; Imperial College; London UK
- Centro Parkinson; Istituti Clinici di Perfezionamento di Milano; Milano Italy
| | - F. C. F. Calboli
- Neuroepidemiology and Ageing Research Unit; School of Public Health; Imperial College; London UK
| | - I. Bravi
- Division of Brain Sciences; Department of Medicine; Imperial College; London UK
| | - D. Gveric
- Division of Brain Sciences; Department of Medicine; Imperial College; London UK
| | - L. K. Curry
- Neuroepidemiology and Ageing Research Unit; School of Public Health; Imperial College; London UK
| | - A. de Smith
- Genomics of Common Disease; School of Public Health; Imperial College; London UK
- Department of Epidemiology and Biostatistics; University of California, San Francisco; San Francisco CA USA
| | - S. Pavlou
- Genomics of Common Disease; School of Public Health; Imperial College; London UK
- Department of Molecular Virology; Cyprus Institute of Neurology and Genetics; Nicosia Cyprus
| | - J. L. Buxton
- Section of Investigative Medicine; Department of Medicine; Imperial College; London UK
| | - A. I. F. Blakemore
- Section of Investigative Medicine; Department of Medicine; Imperial College; London UK
| | - P. Takousis
- Neuroepidemiology and Ageing Research Unit; School of Public Health; Imperial College; London UK
| | - S. Molloy
- Division of Brain Sciences; Department of Medicine; Imperial College; London UK
| | - P. Piccini
- Division of Brain Sciences; Department of Medicine; Imperial College; London UK
| | - D. T. Dexter
- Division of Brain Sciences; Department of Medicine; Imperial College; London UK
| | - F. Roncaroli
- Institute of Brain Behaviour and Mental Health; University of Manchester; Manchester UK
| | - S. M. Gentleman
- Division of Brain Sciences; Department of Medicine; Imperial College; London UK
| | - L. T. Middleton
- Neuroepidemiology and Ageing Research Unit; School of Public Health; Imperial College; London UK
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2
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Economou CN, Vasiliadou IA, Aggelis G, Pavlou S, Vayenas DV. Modeling of oleaginous fungal biofilm developed on semi-solid media. Bioresour Technol 2011; 102:9697-9704. [PMID: 21880483 DOI: 10.1016/j.biortech.2011.08.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/13/2011] [Revised: 07/29/2011] [Accepted: 08/01/2011] [Indexed: 05/31/2023]
Abstract
An oleaginous fungus, Mortierella isabellina, able to transform efficiently sugar to storage lipid, was used as a model microorganism which develops a biofilm structure during the semi-solid fermentation process for the production of biodiesel from sweet sorghum. A mathematical model was developed to describe the fungal oil production in M. isabellina biofilm. The model describes diffusion and consumption of sugars and nitrogen of sweet sorghum and single cell oil production in a biofilm, which grows according to the kinetics of double-substrate limitation (sugars and nitrogen) with sugar inhibition. Experimental data from a previous experimental study were used to determine the kinetic parameters of the model. Maximum biofilm thickness and the percentage of lipid inside the biofilm were estimated using the model at 1892 μm and 15%, respectively. The proposed mathematical model could prove a useful tool for designing semi-solid fermentation processes.
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Affiliation(s)
- Ch N Economou
- Department of Environmental and Natural Resources Management, University of Ioannina, G. Seferi 2, 30100 Agrinio, Greece
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3
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Economou CN, Aggelis G, Pavlou S, Vayenas DV. Single cell oil production from rice hulls hydrolysate. Bioresour Technol 2011; 102:9737-42. [PMID: 21875786 DOI: 10.1016/j.biortech.2011.08.025] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Revised: 07/15/2011] [Accepted: 08/04/2011] [Indexed: 05/05/2023]
Abstract
Rice hull hydrolysate was used as feedstock for microbial lipids production using the oleaginous fungus Mortierella isabellina. Kinetic experiments were conducted in C/N ratios 35, 44 and 57 and the oil accumulation into fungal biomass was 36%, 51.2% and 64.3%, respectively. A detailed mathematical model was used in order to describe the lipid accumulation process. This model was able to predict reducing sugar and nitrogen consumption, fat-free biomass synthesis and lipid accumulation. Neutral lipids constitute the predominant lipid fraction, while the major fatty acids were oleic, palmitic and linoleic acid. Fatty acids of long aliphatic chain were not detected, thus the microbial oil produced is a promising feedstock for biodiesel production.
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Affiliation(s)
- Ch N Economou
- Department of Environmental and Natural Resources Management, University of Ioannina, G. Seferi 2, 30100 Agrinio, Greece
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4
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Economou C, Aggelis G, Pavlou S, Vayenas D. Modeling of single-cell oil production under nitrogen-limited and substrate inhibition conditions. Biotechnol Bioeng 2010; 108:1049-55. [DOI: 10.1002/bit.23026] [Citation(s) in RCA: 91] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2010] [Revised: 11/18/2010] [Accepted: 11/29/2010] [Indexed: 11/11/2022]
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5
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Karanasios KA, Vasiliadou IA, Pavlou S, Vayenas DV. Hydrogenotrophic denitrification of potable water: a review. J Hazard Mater 2010; 180:20-37. [PMID: 20471745 DOI: 10.1016/j.jhazmat.2010.04.090] [Citation(s) in RCA: 165] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2010] [Revised: 04/19/2010] [Accepted: 04/20/2010] [Indexed: 05/29/2023]
Abstract
Several approaches of hydrogenotrophic denitrification of potable water as well as technical data and mathematical models that were developed for the process are reviewed. Most of the applications that were tested for hydrogenotrophic process achieved great efficiency, high denitrification rates, and operational simplicity. Moreover, this paper reviews the variety of reactor configurations that have been used for hydrogen gas generation and efficient hydrogen delivery. Microbial communities and species that participate in the denitrification process are also reported. The variation of nitrate concentration, pH, temperature, alkalinity, carbon and microbial acclimation was found to affect the denitrification rates. The main results regarding research progress on hydrogenotrophic denitrification are evaluated. Finally, the commonly used models and simulation approaches are discussed.
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Affiliation(s)
- K A Karanasios
- Department of Environmental and Natural Resources Management, University of Ioannina, Seferi 2, 30100 Agrinio, Greece
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6
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Dikshitulu S, Baltzis BC, Lewandowski GA, Pavlou S. Competition between two microbial populations in a sequencing fed-batch reactor: theory, experimental verification, and implications for waste treatment applications. Biotechnol Bioeng 2010; 42:643-56. [PMID: 18613087 DOI: 10.1002/bit.260420513] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Competition between two microbial populations for a single pollutant (phenol) was studied in a sequencing fed-batch reactor (SFBR). A mathematical model describing this system was developed and tested experimentally. It is based on specific growth rate expressions revealed from pure culture batch experiments. The species employed were Pseudomonas putida (ATCC 17514) and Pseudomonas resinovorans (ATCC 14235). It was found that both species biodegrade phenol following inhibitory kinetics which can be described by Andrews' expression. The model predicts that the dynamics of a SFBR, and the kinetics of biodegradation, result in a complex set of operating regimes in which neither species, only one species, or both species can survive at steady cycle. The model also predicts the existence of multiple outcomes, achievable from different start-up conditions, in some domains of the operating parameter space. Experimental results confirmed the model predictions. There was excellent agreement between predicted and measured concentrations of phenol, total biomass, and the biomass of each individual species. This study shows how serious discrepancies can arise in scale-up of biodegradation data if population dynamics are not taken into account. It also further confirms experimentally the theory of microbial competition in periodically forced bioreactors.
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Affiliation(s)
- S Dikshitulu
- Department of Chemical Engineering, Chemistry, and Environmental Science, New Jersey Institute of Technology, Newark, New Jersey 07102, USA
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7
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Economou CN, Makri A, Aggelis G, Pavlou S, Vayenas DV. Semi-solid state fermentation of sweet sorghum for the biotechnological production of single cell oil. Bioresour Technol 2010; 101:1385-8. [PMID: 19781936 DOI: 10.1016/j.biortech.2009.09.028] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2009] [Revised: 09/03/2009] [Accepted: 09/08/2009] [Indexed: 05/08/2023]
Abstract
A semi-solid fermentation process for the production of biodiesel from sweet sorghum is introduced. The microorganism used is the oleaginous fungus Mortierella isabellina, which is able to transform efficiently sugar to storage lipid. Kinetic experiments were performed at various water content percentages. The fungus consumed simultaneously sugars and nitrogen contained in sorghum and after nitrogen depletion the biomass growth was completed and oil accumulation began. Water content of 92% presented the highest oil efficiency of 11 g/100 g dry weight of substrate. The semi-solid process is shown to have certain advantages compared to liquid cultures or solid-state fermentation and gives oil of high quality.
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Affiliation(s)
- Ch N Economou
- Department of Environmental and Natural Resources Management, University of Ioannina, G. Seferi 2, 30100 Agrinio, Greece
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8
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Vasiliadou IA, Karanasios KA, Pavlou S, Vayenas DV. Experimental and modelling study of drinking water hydrogenotrophic denitrification in packed-bed reactors. J Hazard Mater 2009; 165:812-824. [PMID: 19054612 DOI: 10.1016/j.jhazmat.2008.10.067] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/09/2008] [Revised: 10/11/2008] [Accepted: 10/15/2008] [Indexed: 05/27/2023]
Abstract
The aim of this work was to study hydrogenotrophic denitrification in packed-bed reactors under draw-fill and continuous operation. Three bench-scale packed-bed reactors with gravel in different sizes (mean diameter 1.75, 2.41 and 4.03 mm) as support media were used, in order to study the effect of particle size on reactors performance. The maximum denitrification rate achieved under draw-fill operation was 4.4 g NO(3)(-)-N/ld for the filter with gravel of 2.41 mm. This gravel size was chosen to perform experiments under continuous operation. Feed NO(3)(-)-N concentrations and hydraulic loadings (HL) ranged between 20-200mg/l and 5.7-22.8m(3)/m(2)d, respectively. A comparison between the two operating modes showed that, for low HL the draw-fill operation achieved higher denitrification rates, while for high HL and intermediate feed concentrations (40-60 mg NO(3)(-)-N/l) the continuous operation achieved higher denitrification rates (4.67-5.65 g/ld). Finally, experiments with three filters in series (with gravels of 4.03, 2.41 and 1.75 mm mean diameter) were also performed under continuous operation. The maximum denitrification rate achieved was 6.2 g NO(3)(-)-N/ld for feed concentration of 340 mg/l and HL of 11.5m(3)/m(2)d. A model, which describes denitrification in packed-bed reactors, was also developed. The model predicts the concentration profiles of NO(3)(-)-N along filter height, in draw-fill as well as in continuous operation, satisfactorily.
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Affiliation(s)
- I A Vasiliadou
- Department of Environmental and Natural Resources Management, University of Ioannina, Agrinio, Greece
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9
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Vasiliadou I, Pavlou S, Vayenas D. Dynamics of a chemostat with three competitive hydrogen oxidizing denitrifying microbial populations and their efficiency for denitrification. Ecol Modell 2009. [DOI: 10.1016/j.ecolmodel.2009.02.009] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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10
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Kavadia A, Vayenas D, Pavlou S, Aggelis G. Dynamics of free-living nitrogen-fixing bacterial populations and nitrogen fixation in a two-prey–one-predator system. Ecol Modell 2008. [DOI: 10.1016/j.ecolmodel.2008.07.018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
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11
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12
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13
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Sgountzos I, Pavlou S, Paraskeva C, Payatakes A. Growth kinetics of Pseudomonas fluorescens in sand beds during biodegradation of phenol. Biochem Eng J 2006. [DOI: 10.1016/j.bej.2006.03.005] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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14
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Vasiliadou IA, Siozios S, Papadas IT, Bourtzis K, Pavlou S, Vayenas DV. Kinetics of pure cultures of hydrogen-oxidizing denitrifying bacteria and modeling of the interactions among them in mixed cultures. Biotechnol Bioeng 2006; 95:513-25. [PMID: 16758460 DOI: 10.1002/bit.21031] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
In this study we report the isolation of four denitrifying bacteria from a batch reactor, where the progress of hydrogenotrophic denitrification was examined. Only three of the strains had the ability to use hydrogen as electron donor. In the present work, kinetic batch experiments were carried out in order to study the dynamic characteristics of pure and defined mixed cultures of hydrogen-oxidizing denitrifying bacteria, under anoxic conditions, in a defined synthetic medium, in the presence of nitrates. Kinetic models were developed and the kinetic parameters were determined from the batch experiments for each bacterium separately. The behavior of mixed cultures and the interactions between the bacteria were described using kinetic models based on the kinetic models developed for each bacterium separately and their predictions were compared with the results from mixed culture experiments. The mathematical models that were developed and validated in the present work are capable of describing the behavior of the bacteria in pure and mixed cultures, and in particular, the kinetics of nitrate and nitrite reduction and cell growth.
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Affiliation(s)
- I A Vasiliadou
- Department of Environmental and Natural Resources Management, University of Ioannina, Seferi 2, 30100 Agrinio, Greece
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15
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Vayenas D, Aggelis G, Tsagou V, Pavlou S. Dynamics of a two-prey–one-predator system with predator switching regulated by a catabolic repression control-like mode. Ecol Modell 2005. [DOI: 10.1016/j.ecolmodel.2005.01.032] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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16
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Abstract
We analyze a mathematical model of a simple food web consisting of one predator and two prey populations in a chemostat. Monod's model is employed for the dependence of the specific growth rates of the two prey populations on the concentration of the rate-limiting substrate and a generalization of Monod's model for the dependence of the specific growth rate of the predator on the concentrations of the prey populations. We use numerical bifurcation techniques to determine the effect of the operating conditions of the chemostat on the dynamics of the system and construct its operating diagram. Chaotic behavior resulting from successive period doublings is observed. Multistability phenomena of coexistence of steady and periodic states at the same operating conditions are also found.
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Affiliation(s)
- D V Vayenas
- Department of Chemical Engineering, University of Patras, FORTH, Greece
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17
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Abstract
We study a model of three microbial populations competing for three complementary nutrients in a single chemostat. By using methods of numerical bifurcation theory we analyze the model equations and determine the effect of the model parameters on the dynamics of the system. The main question to be answered is whether there exist conditions under which the three populations can coexist in a stable state in the chemostat. The analysis shows that coexistence can be obtained as a stable steady state but also as a stable periodic state for a wide range of operating conditions of the chemostat.
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Affiliation(s)
- D V Vayenas
- Department of Chemical Engineering, University of Patras, Greece
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18
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Abstract
The operating diagram of a bioreactor is an illustrative way to present the effect that the operating conditions have on its long-term behavior. It can be constructed if a mathematical model of the bioreactor is available. The procedure for constructing the operating diagram consists in analyzing the dynamic behavior of the system of the differential equations of the model. Some methods are described that can be used in computing operating diagrams of bioreactors. They are based on numerical bifurcation techniques for systems of differential equations. Both cases of bioreactors with constant and periodically varying operating conditions are considered.
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Affiliation(s)
- S Pavlou
- Department of Chemical Engineering, University of Patras, Greece.
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19
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Thomopoulos NA, Vayenas DV, Pavlou S. On the coexistence of three microbial populations competing for two complementary substrates in configurations of interconnected chemostats. Math Biosci 1998; 154:87-102. [PMID: 9949649 DOI: 10.1016/s0025-5564(98)10047-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We examine the question of coexistence of three microbial populations competing for two complementary rate-limiting substrates in configurations of interconnected chemostats. It is known that coexistence of two populations competing for two rate-limiting substrates is possible in a single chemostat, but coexistence is not possible when three populations are involved. We examine whether coexistence of three populations becomes possible by considering configurations of two or three interconnected chemostats, thus allowing for effects of spatial heterogeneity. Computational analysis of the model equations indicates that in the case of two chemostats coexistence is possible only for specific discrete parameter values where the system is structurally unstable and therefore the coexistence state is not practically attainable, whereas in the case of three chemostats coexistence is possible for a whole range of parameter values where the system is structurally stable and therefore the coexistence state can be realized in practice.
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Affiliation(s)
- N A Thomopoulos
- Department of Chemical Engineering, University of Patras, Greece
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20
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Abstract
It is known that, when two microbial populations competing for a single rate-limiting nutrient are grown in a spatially uniform environment, such as a single chemostat, with competition being the only interaction between them, they cannot coexist, but eventually one of the two populations prevails and the other becomes extinct. Spatial heterogeneity has been suggested as a means of obtaining coexistence of the two populations. A configuration of two interconnected chemostats is a simple model of a spatially heterogeneous environment. It has been shown that, when Monod's model is used for the specific growth rates of the two populations, steady-state coexistence can be obtained in such systems for wide ranges of operating conditions. In the present work, we study a model of microbial competition in configurations of interconnected chemostats and we show that, if a substrate inhibition model is used for the specific growth rates of the two populations, coexistence in a periodic state is also possible. The analysis of the model is done by numerical bifurcation theory methods.
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Affiliation(s)
- P Lenas
- Department of Chemical Engineering, University of Patras, Greece
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21
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Sakellariou M, Pavlou S, Tzeferacos A, Michalopoulos J, Kastoras A, Christopoulos J, Papalouka M, Xidias G, Kiessling A. P-100. Outcome of insemination with high sperm concentrations for brief periods of time. Hum Reprod 1997. [DOI: 10.1093/humrep/12.suppl_2.168-a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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22
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Abstract
Coexistence of three microbial populations engaged in pure and simple competition is not possible in a chemostat with time-invariant operating conditions under any circumstances. It is shown that by periodic variation of the chemostat dilution rate it is possible to obtain a stable coexistence state of all three populations in the chemostat. This is accomplished by performing a numerical bifurcation analysis of a mathematical model of the system and by determining its dynamic behavior with respect to its operating parameters. The coexistence state obtained in the periodically operated chemostat is usually periodic, but cases of quasi-periodic and chaotic behavior are also observed.
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Affiliation(s)
- P Lenas
- Department of Chemical Engineering, University of Patras, Greece
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23
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Abstract
Predator-prey systems in continuously operated chemostats exhibit sustained oscillations over a wide range of operating conditions. When two such chemostats interact through flow exchange, the interplay of the oscillation frequencies gives rise to a wealth of dynamic behavior patterns. Using numerical bifurcation techniques, we perform a detailed computational study of these patterns and the transitions between them as the coupling strength and relative frequencies of the two chemostats vary. We concentrate on certain strong resonance phenomena between the two frequencies as well as their mutual extinction and provide a representative sampling of possible phase portraits for our model system. Our observations corroborate recent mathematical results and case studies of coupled nonlinear chemical oscillators in which regions of mutual extinction as well as the Arnol'd structure for two-parameter families of maps of the plane have been observed. We highlight certain unexpected features of the operating diagram discovered through our computational study and discuss their implication for the dynamic response of the chemostat system.
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Affiliation(s)
- M A Taylor
- Department of Chemical Engineering, Princeton University, New Jersey
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24
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Abstract
It is well known that when two microbial populations competing for a single rate-limiting nutrient are grown in a chemostat with time-invariant inputs, with competition being the only interaction between them, they cannot coexist, but eventually one of the two populations prevails and the other becomes extinct. It has been suggested that periodic variation of one of the chemostat's operating parameters can stabilize the coexistence state of the two microbial populations. A systematic numerical study of the model equations describing microbial competition in a chemostat with periodically varying dilution rate is performed, and it is shown that coexistence of the competing microbial populations is obtained for a wide range of operating conditions. The coexistence state is usually in the form of limit cycle oscillations. However, cases of chaotic behavior resulting from successive period doublings and quasi-periodicity are also observed.
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Affiliation(s)
- P Lenas
- Department of Chemical Engineering, University of Patras, Greece
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Pavlou S, Kevrekidis IG. Microbial predation in a periodically operated chemostat: a global study of the interaction between natural and externally imposed frequencies. Math Biosci 1992; 108:1-55. [PMID: 1550993 DOI: 10.1016/0025-5564(92)90002-e] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Predator-prey systems in continuously operated chemostats exhibit sustained oscillations over a wide range of operating conditions. When the chemostat is operated periodically, the interaction of the natural oscillation frequency with the external forcing gives rise to a wealth of dynamic behavior patterns. Using numerical bifurcation techniques, we perform a detailed computational study of these patterns and the transitions (local and especially global) between them as the amplitude and frequency of the forcing vary. The transition from low-forcing-amplitude quasiperiodicity to entrainment of the chemostat behavior by strong forcing (involving the concerted closing of resonance horns) is analyzed. We concentrate on certain strong resonance phenomena between the two frequencies and provide an extensive atlas of computed phase portraits for our model system. Our observations corroborate recent mathematical results and case studies of periodically forced chemical oscillators. In particular, the existence and relative succession of several distinct types of global bifurcations resulting in chaotic transients and multistability are studied in detail. The location in the operating diagram of several key codimension 2 local bifurcations of periodic solutions is computed, and their interaction with an interesting feature we name "real-eigenvalues horns" is examined.
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Affiliation(s)
- S Pavlou
- Department of Chemical Engineering, University of Patras, Greece
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27
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Pavlou S, Vayenas C, Dassios G. Comments on optimal catalyst activity profiles in pellets—VIII. General nonisothermal reacting systems with arbitrary kinetics. Chem Eng Sci 1991. [DOI: 10.1016/0009-2509(91)85041-u] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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28
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Abstract
A mathematical model for an ideal chemostat in which one microbial population feeds on another and where Monod's model is used for the specific growth rates of both populations predicts a less stable behavior for the system than the one observed experimentally. Various factors have been proposed as being the reason for the increased stability of such systems. In this work, the effect of spatial heterogeneity on the dynamics of the microbial feeding interaction is studied. It is concluded that spatial heterogeneity has a stabilizing effect on the system. This effect combined with other factors could be the reason for the increased stability observed in systems where a microbial feeding interaction occurs.
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Affiliation(s)
- E Tsangaropoulou
- Institute of Chemical Engineering and High Temperature Chemical Processes and Department of Chemical Engineering, University of Patras, GR-26110 Patras, Greece
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29
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Pavlou S, Kevrekidis IG, Lyberatos G. On the coexistence of competing microbial species in a chemostat under cycling. Biotechnol Bioeng 1990; 35:224-32. [DOI: 10.1002/bit.260350303] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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30
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Mortola JF, Sathanandan M, Pavlou S, Dahl KD, Hsueh AJ, Rivier J, Vale W, Yen SS. Suppression of bioactive and immunoreactive follicle-stimulating hormone and luteinizing hormone levels by a potent gonadotropin-releasing hormone antagonist: pharmacodynamic studies. Fertil Steril 1989; 51:957-63. [PMID: 2498133] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Dose-dependent gonadotropin suppression by a potent gonadotropin-releasing hormone (GnRH) antagonist, Nal1 Glu6 [( Ac-D2Nal1,D4ClPhe2,D3Pal3,Arg5,DGlu(AA)6,- DAla10]GnRH), was determined in five postmenopausal women by frequent sampling for immunoreactive luteinizing hormone (I-LH) and immunoreactive follicle stimulating hormone (I-FSH) for 72 hours after single intramuscular (IM) injections of 10, 50, 150, and 300 micrograms/kg. Bioactive (B) LH and B-FSH also were measured after the IM administration of the 50-micrograms/kg dose. Serum levels of Nal1 Glu6 were determined by a radioreceptor assay for the first 24 hours after the 50-micrograms/kg IM dose and in three women after a 10-micrograms/kg intravenous (IV) dose. While the disappearance rate of serum Nal1 Glu6 after a 10-micrograms/kg IV injection was rapid, gonadotropin suppression persisted longer than detectable serum levels. In contrast, after a 50-micrograms/kg IM injection, the decline from peak circulating levels was slower, contributing to its longer duration of action (greater than 24 hours). All IM doses tested resulted in a similar 51% to 63% decrease in I-LH, which was maximal by 8 hours. The duration of action was dose-dependent, with decreased levels lasting up to 72 hours at the 300-micrograms/kg dose. While decline of I-FSH was smaller (14% to 33%), the duration of suppression was also dose-dependent, although the nadir occurs later (8 to 9 hours after administration) and suppression lasted longer (72 hours at the 150-micrograms/kg dose). The reduction of B-LH was greater than that of I-LH and the suppression of B-FSH also was greater than that of I-FSH.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- J F Mortola
- Department of Reproductive Medicine, University of California, San Diego, School of Medicine, La Jolla 92093
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Sambanis A, Pavlou S, Fredrickson AG. Coexistence of bacteria and feeding ciliates: Growth of bacteria on autochthonous substrates as a stabilizing factor for coexistence. Biotechnol Bioeng 1987; 29:714-28. [DOI: 10.1002/bit.260290608] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Abstract
The effects of the potent GnRH antagonist [Ac-D-NAL(2)1, 4F-D-Phe2, D-Trp3, D-Arg6]-GnRH (GnRH-A), on ovulation in mature rats and rabbits and on serum LH and FSH levels in ovariectomized rats, rabbits and mice were investigated. Dose-response studies showed that 1 microgram (4 micrograms/kg) of GnRH-A was sufficient to inhibit ovulation completely in cycling rats, while 500 micrograms (135 micrograms/kg) were required to inhibit mating induced ovulation in 8 of 11 rabbits. Two of the 3 rabbits which ovulated in spite of the antagonist treatment had delayed LH surges. The mean LH peak of these 3 rabbits was significantly (p less than 0.001) lower than that of controls. Pituitary response to GnRH-A, as measured by plasma gonadotropin levels following GnRH-A treatment in ovariectomized rabbits, rats and mice showed highest sensitivity of the rat to the inhibitory effects of the antagonist. Serum FSH levels were slightly suppressed in rats, but remained undiminished in rabbits and mice. The difference in the response of the three species to the antipituitary effects of GnRH-A is most likely due to differences in the affinity of the pituitary GnRH receptor to the antagonist.
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Wang NG, Sundaram K, Pavlou S, Rivier J, Vale W, Bardin CW. Mice are insensitive to the antitesticular effects of luteinizing hormone-releasing hormone agonists. Endocrinology 1983; 112:331-5. [PMID: 6291919 DOI: 10.1210/endo-112-1-331] [Citation(s) in RCA: 57] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Treatment of male rats with [(imBzl)-D-His6, Pro9-NEt]LHRH or [D-Trp6,Pro9-NEt]LHRH, potent agonists of LHRH, led to a marked decrease in serum testosterone levels and a reduction in testicular LH receptor concentration. Similar treatment of mice showed that they were resistant to the antitesticular effects of the LHRH agonists. To further explore the differences between rats and mice, the direct antitesticular effects of these peptides were investigated in hypophysectomized animals. Hypophysectomized rats and mice were given ovine FSH (50 micrograms), with or without a LHRH agonist (10 micrograms), daily for 5 days. On day 6, the testicular steroidogenic response to hCG was studied. In these studies the in vivo as well as the in vitro steroidogenic response of rat testes to hCG were inhibited by the LHRH analogs. In contrast, pretreatment of mice with the LHRH analogs did not affect their testicular steroidogenic response. Binding studies with the [125I]LHRH analog demonstrated receptors for this peptide on Leydig cells from adult rats. Receptors for LHRH were not, however, detectable on murine Leydig cells. These results suggest that one of the reasons for the lack of an antitesticular effect of LHRH agonists in mice may be due to the inability of these peptides to have a direct effect on testes and may relate to a lack of LHRH receptors.
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Benelli C, Durbin P, Pavlou S, Michel O, Michel R. [Effects of thyroidectomy on the limiting step of steroid biosynthesis in the adrenal cortex and testis of the rat]. Pathol Biol (Paris) 1980; 28:371-372. [PMID: 6994041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
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Batrinos ML, Panitsa-Faflia C, Pitoulis S, Pavlou S, Piaditis G, Alexandridis T, Liappi C. The clinical features of the menopause and its relation to the length of pregnancies and lactation. Maturitas 1979; 1:261-8. [PMID: 551236 DOI: 10.1016/0378-5122(79)90016-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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