共查询到20条相似文献,搜索用时 15 毫秒
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Niels Nyholm 《Biotechnology and bioengineering》1977,19(4):467-492
The kinetics of phosphate limited growth of two green algae Chorella pyrenoidosa and Selenastrum capricornutum have been studied in chemostats. Several kinetic models which express the specific growth rate as a function of the intracellular phosphours content have been examined, and one of the models was found to be significantly better than the other models. The principles of this model were described in a recent paper by Nyholm. The kinetics of phosphate uptake have been investigated by adding pulses of phosphate to the chemostats. The uptake by phosphours deficient cells could be described by Michaelis–Menten kinetics for phosphate concentrations below approximately 500 μg P/liter. Further, with the assumption of a discontinuous adjustment of the uptake rate at the onset of phosphours deficiency, a complete kinetic model for growth and phosphate removal is proposed. The mean cell size and the contents of chlorophyll and RNA per unit dry weight have been measured for C. pyrenoidosa as a function of the dilution rate. 相似文献
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Piotr Skupin 《Journal of biological dynamics》2018,12(1):663-682
The paper discusses the possibility of using a mixture of two growth limiting substrates to induce or eliminate self-sustained oscillations in a continuous culture process. The proportion of both substrates in the mixture is treated as a new control variable. The presented approach is based on the assumption that the oscillatory behaviour occurs for selected substrates in some range of dilution rates. Because a double-substrate limitation may occur, the analysis is performed for two fundamental substrate utilization patterns: simultaneous consumption and diauxic growth. By using model simulations and bifurcation analysis, we show that an appropriate proportion of two substrates in the mixture allows for the control of the oscillatory behaviour. 相似文献
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Based on present knowledge to growth of Methanococcus capsulatus a model for the nitrogen limited growth in a chemostat with ammonia as nitrogen source is proposed. The model may predict excretion of nitrate and nitrite with excess of ammonia in broth. 相似文献
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The paper is concerned with the results of comparative analysis of the clinical, x-ray and cytological methods of investigation of women with breast tumors in situ (43 cases of cancer and 19 cases of intracanalicular fibroadenoma, the latter being difficult for differential diagnosis). A number of important diagnostic symptoms were identified. Cancer affected more frequently women over 55. It was characterized by the presence of microcalcinates (60 +/- 13%) and inadequacy of tumor sizes on palpation and on radiograms (35 +/- 7%). The diagnostic accuracy of the methods used separately was 44 +/- 8% for the clinical method, 79 +/- 7% for the x-ray method, and 89 +/- 3% for the cytological method. Their combined use in a specialized mammography unit resulted in 98 +/- 2% of diagnostic accuracy. 相似文献
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Spatially extended catalyst-induced growth processes are studied. This type of processes exists in all domains of biology, ranging from ecology (nutrients and growth), through immunology (antigens and lymphocytes) to molecular biology (signaling molecules initiating signaling cascades). The extinction-proliferation transition is considered for a system containing discrete catalysts (A) that induces the proliferation of a discrete reactant (B). The realization of this model on an infinite capacity d-dimensional discrete lattice for immortal catalysts has been previously considered (the AB model). It was shown that the adaptation of the reactants to the diffusive noise induced by stochastic fluctuations of catalyst density yields proliferation even if the average environmental conditions lead to extinction. This model is extended here to include more realistic situations, like finite lifespan of the catalysts and finite carrying capacity of the reactants. By using a combination of Monte Carlo simulation, percolation-theory-based estimations and an analytic perturbative analysis, the asymptotic behavior of these systems is studied. In both cases studied, it turns out that the overall survival of the reactant population at the long run is based on the size and shape of a typical single colony, related to the localized proliferation around spatio-temporal catalyst density fluctuations. If the density of these colonies (based on the lifetime of the spatial fluctuation and the carrying capacity of the medium) is large enough, i.e. above the percolation threshold, the reactant population survives even in (on average) hostile environment. This model provides a new insight on the population dynamics in chemical, biological and ecological systems. 相似文献
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Amino acid limited growth of starter cultures in milk 总被引:2,自引:0,他引:2
The specific growth rates of several Streptococcus cremoris strains were 10–40% lower in milk than in other growth in media. The growth rates in milk increased when an amino acid mixture or casein was added, whereas, when milk was diluted, the specific growth rate of the streptococci decreased. This decrease could be overcome by bringing the casein concentration in the diluted milk back to the normal value (3%). This indicates that casein-hydrolysis proceeded at a rate too low for the streptococci to reach their potential maximum specific growth rates in milk so that growth in milk is essentially amino acid-limited. This was subsequently demonstrated for S. cremoris by continuous cultivation in media with low casein concentrations. At a low dilution rate casein hydrolysis was fast enough to supply the cells with enough amino acids and lactose was growth-limiting, whereas at higher dilution rates amino acids became growth-limiting. In cultures exponentially growing in milk the concentration of free amino acids was measured to determine which amino acid(s) was(were) absent and could possibly limit growth. A number of essential amino acids (leucine, methionine, glutamate and in some cases phenylalanine) were not detected and addition of these, together, stimulated the growth of S. cremoris in milk. The amino acids leucine and phenylalanine appeared to play a particularly important role in this stimulation. These two are, supposedly, the first amino acids that become limiting during growth in milk. The effect of competition for casein and amino acids by different organisms was studied in continuous cultures. At different dilution rates different strains became dominant in these mixed cultures, suggesting that differences in apparent affinity constants (KS) for casein, leucine and glutamate existed between the strains. 相似文献
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Summary The linear growth phase in cultures limited by intracellular (conservative) substrate is represented by a flat exponential curve. Within the range of experimental errors, the presented model fits well the data from both batch and continuous cultures ofEscherichia coli, whose growth is limited in that way.List of symbols D
dilution rate, h–1
- KS
saturation constant, g.L–1
- S
concentration of the limiting substrate, g.L–1
- Si
concentration of the limiting substrate accumulated in the cells, g.g–1
- So
initial concentration of the limiting substrate, g.L–1
- t
time of cultivation, h
- t1
time of exhaustion of the limiting substrate from medium, h
- to
beginning of exponential phase, h
- X
biomass concentration, g.L–1
- X1
biomass concentration at the time of exhaustion of the limiting substrate from the medium, g.L–1
- Xo
biomass concn. at the beginning of exponential phase, g.L–1
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biomass concn. at steady-state, g.L–1
- Y
growth yield coefficient (biomass/substrate)
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specific growth rate, h–1
- m
maximum specific growth rate, h–1 相似文献
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Niels Nyholm 《Journal of theoretical biology》1978,70(4):415-425
A simulation model is suggested which describes transient growth of the green alga Chlorella pyrenoidosa after exposure of phosphate limited chemostatic cultures to phosphate shocks. The specific growth rate is related to an internal concentration of functional phosphorus. The model includes a metabolic activity functional as suggested by Powell (1969), and it is assumed that phosphate taken up by the cells passes through an intermediate pool of not functional phosphorus which is thought to inhibit growth. Comparisons are made with a simpler model described previously. 相似文献
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Iron uptake and iron limited growth of Escherichia coli K-12 总被引:4,自引:0,他引:4
Cells of Escherichia coli K-12 could grow aerobically at an iron concentration as low as 0.05 M without any of the known iron ionophores present. The growth rate increased between 0.05 and 2 M iron. Supplementation with the iron ligands ferrichrome and citrate resulted in optimal growth already at 0.05 M iron. Under certain conditions iron uptake preceded growth of cells by more than an hour. During logarithmic growth the rate of iron uptake matched the growth rate. The radioactive tracer method revealed a cellular iron content of 4 nmol/mg dry weight.After consumption of the iron in the medium cells continued to grow with high rate for 1–2 generations. The iron uptake activity was increased during iron starvation. 相似文献
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M A Zaval'ny? V P Grachev L L Mironova 《Biulleten' eksperimental'no? biologii i meditsiny》1984,97(4):462-465
An original technique was used to study the growth pattern of cells of varying origin on limited areas (from 1 to 0.01 mm2). During cultivation on limited areas, the growth of primary and continuous fibroblast-like cells was inhibited, whereas that of normal and transformed epithelioid cells was not. The growth of fibroblast-like skin cells of diploid lines and human embryonal muscles was completely inhibited in cultivation on 0.1-0.02 mm2 areas and partially inhibited in cultivation on 0.03-0.16 mm2 areas. Other normal fibroblast-like cells used in the experiment were also marked by growth inhibition of varying degree during cultivation on limited areas. The technique suggested and the data thus obtained may be used for studying substrate-cell and cell-cell interactions, selection of epithelioid cells, and the development of optimal microcarrier technology for cell cultures. 相似文献
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AIMS: Using limited digital image sampling, a model of fungal growth in soil that considers both hyphal production and lysis was constructed for two strains of Trichoderma virens over a range of four temperatures. MATERIALS AND METHODS: A growth model was developed by fitting the radial cross sectional data with a modified form of the Ratkowsky equation to determine maximum growth rate and a modified Arrhenius equation to determine maximal rate of decrease in area covered by mycelia. The parameters obtained from a combined equation were then verified by using the data obtained from the whole colony to determine the appropriateness of the model. CONCLUSIONS: Using a limited data set and a combination of the Ratkowsky and Arrhenius equations, the mycelial coverage of the T. virens colony was determined, relating microscopic hyphal growth to macroscopic colony growth. This model was sufficiently robust to predict growth across four temperatures for a genetically modified and wild-type strain of T. virens. SIGNIFICANCE AND IMPACT OF STUDY: By using simple assumptions for the increase and eventual decline in fungal growth on a resource-limited medium, this model constructs an initial framework onto which additional parameters such as nutrient consumption could be incorporated for prediction of fungal growth. 相似文献
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This report continues our research into the effectiveness of adaptive synaptogenesis in constructing feed-forward networks
which perform good transformations on their inputs. Good transformations are characterized by the maintenance of input information
and the removal of statistical dependence. Adaptive synaptogenesis stochastically builds and sculpts a synaptic connectivity
in initially unconnected networks using two mechanisms. The first, synaptogenesis, creates new, excitatory, feed-forward connections.
The second, associative modification, adjusts the strength of existing synapses. Our previous implementations of synaptogenesis
only incorporated a postsynaptic regulatory process, receptivity to new innervation (Adelsberger-Mangan and Levy 1993a, b).
In the present study, a presynaptic regulatory process, presynaptic avidity, which regulates the tendency of a presynaptic
neuron to participate in a new synaptic connection as a function of its total synaptic weight, is incorporated into the synaptogenesis
process. In addition, we investigate a third mechanism, selective synapse removal. This process removes synapses between neurons
whose firing is poorly correlated. Networks that are constructed with the presynaptic regulatory process maintain more information
and remove more statistical dependence than networks constructed with postsynaptic receptivity and associative modification
alone. Selective synapse removal also improves network performance, but only when implemented in conjunction with the presynaptic
regulatory process.
Received: 20 August 1993/Accepted in revised form: 16 April 1994 相似文献
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Summary An extension to the model previously presented by Brown et al. (1988) is developed for the case of a conserved substrate that is incorporated into the cell structure. It is shown that the model can predict both an inflection point and a period of essentially linear growth. Effects of the adjustable parameters and the ability to predict experimental results are determined. 相似文献