Mutation in continuous cultures of Schizosaccharomyces Pombe. I. Dependence of the kinetics of mutation accumulation upon the growth-limiting nutrilite

The rate of spontaneous mutation to resistance to the 12,13-epoxytrichothecene trichodermin has been determined under different growth limiting conditions in continuous cultures of the microbial eukaryote Schizosaccharomyces pombe. In agreement with data obtained in bacterial systems by previous workers the kinetics observed for the accumulation of mutations is found to be dependent upon the nutrient used to limit the growth of the population. Under conditions of glucose-limitation mutation accumulation is directly proportional to the rate of cell division, while under histidine-limitation it is proportional to chronological time. Various possible explanations for these observations are discussed.     

Kinetic analysis of template-instructed and de novo RNA synthesis by Q beta replicase

The kinetics of template-free and template-instructed RNA synthesis by Q_β replicase were investigated. Template-instructed RNA synthesis has different growth rates in the exponential (excess enzyme) and the linear (excess template) phase of growth. In the absence of exogenous template, Q_β replicase synthesizes self-replicating RNA after an initial lag phase (“template-free” synthesis). The lag time can be determined by extrapolating the growth curve to the time of appearance of the first self-replicating strand. Growth rates in the exponential and linear phase, and especially the times of the lag phase for nucleotide incorporations under identical template-free conditions, show considerable scattering in contrast to the deterministic behavior of template-instructed synthesis. Evaluation of the kinetic data reveals that the time lag of template-free synthesis is strongly dependent on the concentration of the nucleoside triphosphate and the enzyme. The lag time is approximately inversely proportional to the powers 2.75 of the nucleotide and 2.5 of the enzyme concentration, respectively, both being lower limit values. The rate of template-instructed RNA synthesis is linearly proportional to the enzyme concentration and less than linearly proportional to the triphosphate concentration, in accordance with a substrate dependence of a Michaelis-Menten type of mechanism. The kinetic data cannot be reconciled with the proposition that template-free synthesis is due to low concentrations of templates present as impurities in the incorporation mixture and giving rise to autocatalytic RNA synthesis by a template-instructed mechanism. The data strongly favor the de novo mechanism proposed by Sumper &; Luce (1975).     

Oxygen requirement in pullulan fermentation

Summary Oxygen was essential for the biosynthesis of pullulan by Aureobasidium pullulans. In a growth medium, pullulan yield and synthesis rate were proportional to the oxygen availability. However, under controlled oxygen environment in a non-growth medium, the synthesis rate and the yield of pullulan were inversely proportional to the oxygen tension. A relationship between melanin production and oxygen transfer conditions was also observed. The elapsed time prior to the appearance of the pigment was dependent upon the degree of oxygen availability.     

不同刈牧强度对冷蒿生长与资源分配的影响

利用野外实验与盆栽实验,对不同刈牧强度下冷蒿生长与资源分配影响的研究结果表明,按比例刈割冷篙的再生生长大于留茬高度刈割,在生长季前期,不刈割冷蒿净生长高于刈割处理,而进入生长季中后期(8月中旬以后),轻度刈割净生长高于不刈割处理,冷篙种群生物量分配的总体格局是根>叶>茎,刈牧明显影响冷蒿生物量分配格局,尤其是叶和花的分配,3／4刈割或留茬4cm刈割叶生物量分配显著高于其它各处理,而花的生物量及其分配显著低于其它处理,根、茎生物量分配各处理间差异不显著．冷蒿有性生殖分配随刈牧强度的增加而降低,繁殖方式发生了改变,优先将光合产物分配给再生茎以及繁殖方式转向营养繁殖,通过克隆生长维持和扩大种群是冷蒿对强度放牧的生态适应对策。     

A Mathematical Model for the Effect of Water Pollutants on the Growth Pattern of Pollen

The heavy metals as water pollutants had some adverse effects on the growth pattern of pollen grains of the aquatic macrophytes viz. Ottelia, Vallisneria, Hyderilla and Eichhornia. The germination of pollen grains were inversely proportional and the abnormality of pollen tube and the flowering time were directly proportional to the concentration of the heavy metal. In this paper we have presented a mathematical model that is the germinability and the abnormality changes with the log-value of concentration in a straight line fashion. Also the flowering time changes with treatment time in an exponential pattern.     

Theory of the mitotic index and its application to tissue growth measurement

Analysis is made to show that the mitotic index is simply proportional to the ratio of the duration of mitosis (T) to the intermitotic time only under special conditions. In the case of exponential growth of cell population the simple proportionality hold if the product ofT and the growth constant is small. For power law (t ⁿ ) growth of cell population the simple proportionality holds only when a steady state of growth has existed for at least ten intermitotic periods. The simple proportionality does not apply in conditions of transient growth. This document is based on work performed at Los Alamos Scientific Laboratory of the University of California under government contract W-7405-eng-36 and the information contained therein will appear in Division V of the National Nuclear Energy Series (Manhattan Project Technical Section) as part of the contributions of the Los Alamos Laboratory.     

Analysis of correlation between some parameters depending on cell proliferation and life span of "stationary phase aging" cultures and maximum life span of mammals

Earlier we developed a "stationary phase aging" model and introduced a definition of life span of "stationary phase aging" cell cultures. In this model the cells grow after seeding in flasks without subcultivation and medium change. They reach cell saturation density, stop dividing, gradually degrade ("stationary phase aging") and perish. By the term "culture life span" we designate the time from cell seeding until culture death. We designate the culture as dead when the number of living cells is less than 10 per cent of their number at saturation density of cell culture. The life span of transformed Chinese hamster cells was found to be proportional to the duration of their growth from cell seeding up to saturation density, as well as to the number of cell culture doublings and to be inversely proportional to the velocity of cell culture doubling for the same growth period. Maximum life span of mammals is known to be proportional to pregnancy duration and to the age at puberty. We found that maximal life span of mammals was proportional to the number of cell population doublings and inversely proportional to the velocity of cell population doubling during embryonal period or for the time from zygote to growth termination. The dependences for cell cultures and for mammals are analogous to each other.     

Mixotrophic Growth of Hydrogenomonas eutropha

Mixotrophic growth conditions were established by the addition of lactate to cultures of Hydrogenomonas eutropha growing autotrophically in a gaseous environment of H(2), O(2), and CO(2) (6:2:1). The specific growth rate of mixotrophic cultures was double that of the autotrophic cultures, and lactate disappearance paralleled growth. Growth yields in mixotrophic cultures were significantly greater than those in heterotrophic cultures for equal quantities of lactate consumed. The magnitude of the increase in yield was directly proportional to the absolute growth rate at the time of lactate addition to the starting autotrophic culture and to the time under mixotrophic conditions. The specific activities of hydrogenase and ribulose diphosphate carboxylase decreased during mixotrophic growth; the total activities increased somewhat. The results suggested that the complete autotrophic and heterotrophic physiologies functioned simultaneously under mixotrophic contions.     

Specific growth rate of Chlamydomonas reinhardtii and Chlorella sorokiniana under medium duration light/dark cycles: 13–87 s

The specific growth rate of Chlamydomonas reinhardtii and Chlorella sorokiniana decreased under square-wave light/dark cycles of medium duration, 13–87 s, in comparison to continuous illumination. Three experiments were done in three different turbidostats at saturating and sub-saturating light intensities during the light period, 240–630 μmol m⁻² s⁻¹. Within each experiment the light intensity during the light periods of the intermittent light regimes was equal and this intensity was also applied under continuous illumination. The specific growth rate decreased proportional or more than proportional to the fraction of time the algae were exposed to light; this light fraction ranged from 0.32 to 0.88. We conclude that under these light regimes the chlorophyta C. reinhardtii and C. sorokiniana are not able to store light energy in the light period to sustain growth in the dark period at the same rate as under continuous illumination. C. reinhardtii increased its specific light absorbing surface by increasing its chloropyll-a content under light/dark cycles of 13 s duration and a light fraction of 0.67 at 240 μmol m⁻² s⁻¹; the chloropyll-a content was twice as high under intermittent illumination in comparison to continuous illumination. The combination of a higher specific light absorption together with a lower specific growth rate led to a decrease of the yield of biomass on light energy under intermittent illumination.     

Surface-limited growth: a model for the synchronization of a growing bacterial culture through periodic starvation

This article analyses the Surface-Limited Growth Model put forward to explain the very tight synchrony, over more than ten division cycles, obtained experimentally by subjecting a growing bacterial culture to alternating periods of starvation and dilution, using inorganic phosphate as the limiting substrate. The Model states that when an essential nutrient is in limited supply, the rate of growth of an individual cell will be proportional to its surface area (and the current concentration of the limiting substance) rather than to its volume. This decrease in dimensionality from volume to surface is expected to favor the smaller cells and so result ultimately in a narrower size distribution. The Surface-Limited Growth Model deals with cell growth under unusual nutritional conditions, and its predictions depend on how the cell replication cycle is assumed to behave under these same circumstances. Two alternatives are considered: the volume at which cells divide is the same during the starvation phase as during steady-state exponential growth, and the cells adjust immediately to the changing growth rate. In the latter case, we have tested both C + D constant with time and C + D variable (where C + D is the time between initiation of chromosome replication and the corresponding cell division), the incremental value at any instant being computed separately for each individual cell from its current effective growth rate. The simulation results are of two sorts depending on the auxiliary assumptions used. Either the dilution-starvation cycles have no effect whatsoever on the cell volume distribution, or the width of the distribution decreases gradually with time, approaching zero slowly and asymptotically, but the mean cell volume decreases as well--directly contradicting experimental observations. We conclude that the Surface-Limited Growth Model is incapable of explaining the synchronization of cells by periodic starvation of a growing bacterial culture.     

Growth and anthocyanin production by carrot suspension cultures grown under chemostat conditions with phosphate as the limiting nutrient

Chemostat cultures of carrot suspension cultures, where growth was limited by the concentration of phosphate in the input medium, were achieved by replacing a fixed proportion of the culture with fresh medium at daily intervals. In the range 0.05–0.30mM phosphate in the input medium and at a specific growth rate of 0.357 days^?1, steady-state culture density but not anthocyanin in the cells was strictly proportional to the input phosphate concentration with no intercept. At a phosphate concentration of 0.10mM and growth rates from 0.105 to 0.430 days^?1, the steady-state culture density could not be described by Monod's model of chemostat cultures, but could be described by Nyholm's model. The steady-state levels of anthocyanin were not strictly proportional to the steady-state biomass under all conditions, showing that anthocyanin production is not completely growth associated.     

Effect of light and nutrients on biomass allocation in Calamagrostis canadensis

The effects of light intensity and nutrient availability on the biomass allocation of Calamagrostis canadensis were studied under both greenhouse and field conditions In the greenhouse, seedlings from forest and wetland populations were grown in sand-peat mixtures, under three light intensities and three fertilizer levels Total above and below ground growth increased with light intensity and nutrient availability, nutrient availability, however, only altered plant growth when light intensity was above moderate levels Numbers of rhizomes were greatest under low and moderate nutrient regimes but high light was also needed for maximum numbers of rhizomes In the field, tillers and rhizomes were examined under open, 40% and 85% canopy cover Tiller and rhizome weight and diameter of rhizomes decreased with canopy closure However, proportional allocation of biomass to rhizomes was greatest and percentage total non-structural carbohydrates of rhizomes was lowest under a 40% canopy     

Growth of an Ethane-utilizing Mixed Culture in a Chemostat

Bacteria capable of utilizing ethane as their sole source of carbon and energy at 42° were readily isolated from soil samples obtained from Brunei with batch culture enrichment techniques. No ethane utilizers capable of growth at 42° were isolated, however, from soil samples obtained from Britain. An ethane-utilizing mixed culture was grown under ammonia limitation in chemostat culture. The lipid content of the culture was inversely proportional to the dilution rate. Similarly, the amount of organic carbon excreted into the culture supernatant was inversely proportional to the growth rate and could be accounted for mainly as carbohydrate. The specific rates of ethane and oxygen consumption, carbon dioxide production and yield from ethane were directly proportional to the dilution rate.     

Changes in Cell Size and Shape Associated with Changes in the Replication Time of the Chromosome of Escherichia coli

Average cell mass is shown to be inversely related to the concentration of thymine in the growth medium of a thy⁻ strain of Escherichia coli. The kinetics of the transition from one steady-state average cell mass to another was followed in an attempt to determine the relationship between the chromosome replication time and the time between completion of a round of chromosome replication and the subsequent cell division. Differences in average cell mass are shown to be associated with similar differences in average cell volume. Changes in volume associated with changes in thymine concentration are shown to be due primarily to differences in the width of cells. It is proposed that extension in length of the cell envelope occurs at a linear rate which is proportional to the growth rate and which doubles at the time of termination of rounds of replication. Changes in volume not associated with a change in growth rate are therefore accommodated by a change in cell width. Conditions are described under which average cell mass can continue to increase in successive generations and no steady-state average cell mass is achieved.     

On the vegetative biomass partitioning of seed plant leaves, stems, and roots

A central goal of comparative life-history theory is to derive the general rules governing growth, metabolic allocation, and biomass partitioning. Here, we use allometric theory to predict the relationships among annual leaf, stem, and root growth rates (GL, GS, and GR, respectively) across a broad spectrum of seed plant species. Our model predicts isometric scaling relationships among all three organ growth rates: GL is proportional to GS is proportional to GR. It also provides a conceptual basis for understanding the differences in the absolute amounts of biomass allocated to construct the three organ types. Analyses of a large compendium of biomass production rates across diverse seed plant species provide strong statistical support for the predictions of the theory and indicate that reproductive investments may scale isometrically with respect to vegetative organ growth rates. The general rules governing biomass allocation as indexed by the scaling exponents for organ growth rates are remarkably indifferent to plant size and taxonomic affiliation. However, the allometric "constants" for these relationships differ numerically as a function of phenotypic features and local environmental conditions. Nonetheless, at the level of both inter- and intraspecific comparisons, the same proportional biomass allocation pattern holds across extant seed plant species.     

A mechanism of microbial cell growth

Presently empirical expressions, especially the Monod equation, are used to quantitatively relate microbial growth rate to limiting substrate concentration in the solution. In this paper microbial growth is postulated to occur by a mechanism involving a mass transfer or assimilation process. The assimilation process is assumed to be substrate mass transfer limited and hence proportional to the limiting substrate concentration. The ingestion is assumed independent of limiting substrate concentration and only dependent upon internal reaction rates. The quantitative relationship between limiting substrate and microbial growth rate resulting from this mechanism is developed. Under certain limiting conditions this expression is shown to reduce to the Monod equation and under other conditions it reduces to the Lotka-Volterra relationship. This mechanism is applied to batch and continuous cultures and the results obtained are compared quantitatively with experiment.     

Mammalian growth and development parameters, cell proliferation in culture and the maximal life span]

The maximum life span of mammals is known to be proportional to the pregnancy duration and to the age at puberty. We found that the maximum life span of mammals was also proportional to the number of cell doublings, and inversely proportional to the rate of duplication of these cells, during embryogenesis or for the time from zygote formation to growth termination. We found also that the life span of "stationary phase aging" transformed Chinese hamster cells (time from subcultivation until culture "death", i.e., until the moment when the number of live cells is less than 10% of their number at saturation density) was proportional to the duration of their growth and number of cell doublings during the period from subcultivation to saturation density, and inversely proportional to the rate of cell culture duplication during the same period. The dependencies for cell cultures and mammals proved to be analogous to each other. An approximately twofold decrease in the cell duplication rate, as a result of a decrease of the growth medium temperature from 37 to 27 degrees C or the introduction of ethanol to a final concentration 2%, increased the life span of "stationary phase aging" cultures more than twofold. The data obtained suggest that influences resulting in optimized delay of the rate of cell duplication, and correspondingly the mean rate of proliferation during the period of growth in mammals, may increase their maximum life span.     

Control of cell length in Bacillus subtilis.

During inhibition of deoxyribonucleic acid synthesis in Bacillus subtilis 168 Thy-minus Tryp-minus, the rate of length extension is constant. A nutritional shift-up during thymine starvation causes an acceleration in the linear rate of length extension. During a nutritional shift-up in the presence of thymine, the rate of length extension gradually increases, reaching a new steady state at about 50 min before the new steady-state rate of cell division is reached. The steady-state rates of nuclear division and length extension are reached at approximately the same time. The ratio of average cell length to numbers of nuclei per cell in exponential cultures is constant over a fourfold range of growth rates. These observations are consistent with: (i) surface growth zones which operate at a constant rate of length extension under any one growth condition, but which operate at an absolute rate proportional to the growth rate of the culture, (ii) a doubling in number of growth zones at nuclear segregation, and (iii) a requirement for deoxyribonucleic acid replication for the doubling in a number of sites.     

A mathematical model to study the effects of drugs administration on tumor growth dynamics

A mathematical model for describing the cancer growth dynamics in response to anticancer agents administration in xenograft models is discussed. The model consists of a system of ordinary differential equations involving five parameters (three for describing the untreated growth and two for describing the drug action). Tumor growth in untreated animals is modelled by an exponential growth followed by a linear growth. In treated animals, tumor growth rate is decreased by an additional factor proportional to both drug concentration and proliferating cells. The mathematical analysis conducted in this paper highlights several interesting properties of this tumor growth model. It suggests also effective strategies to design in vivo experiments in animals with potential saving of time and resources. For example, the drug concentration threshold for the tumor eradication, the delay between drug administration and tumor regression, and a time index that measures the efficacy of a treatment are derived and discussed. The model has already been employed in several drug discovery projects. Its application on a data set coming from one of these projects is discussed in this paper.     

Kinetics of human lymphocyte responses in vitro: the phase of exponential growth

The kinetics of thymidine uptake in human peripheral lymphocytes stimulated by allogenic cells, antigen E (ragweed allergen) and a variety of mitogens can generally be divided into four consecutive phases. First, a lag period with no increase in thymidine uptake, then a short period of rapid change in uptake, followed by a log-linear growth period and finally a decay phase. In this report we examine in detail the characteristics of the third, log-linear growth phase. Since, as discussed in the preceding paper, thymidine uptake is proportional to the number of cells acumulating thymidine, we can calculate from the log-linear growth period an apparent doubling time. We show that for five different stimulating agents the cells reach a log-linear growth phase of varying length and that the doubling times show little variation. This invariance indicates that, despite possible variation in cell death and recruitment rates, the rate of proliferation is in all cases dominated by the generation time of human lymphocytes.