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Maximum Growth Rate (maximum + growth_rate)

Distribution by Scientific Domains

Life Sciences	83%
Earth and Environmental Science	16%

Selected Abstracts

Maximum growth rates and possible life strategies of different bacterioplankton groups in relation to phosphorus availability in a freshwater reservoir

ENVIRONMENTAL MICROBIOLOGY, Issue 9 2006
Karel, imek
Summary We investigated net growth rates of distinct bacterioplankton groups and heterotrophic nanoflagellate (HNF) communities in relation to phosphorus availability by analysing eight in situ manipulation experiments, conducted between 1997 and 2003, in the canyon-shaped ,ímov reservoir (Czech Republic). Water samples were size-fractionated and incubated in dialysis bags at the sampling site or transplanted into an area of the reservoir, which differed in phosphorus limitation (range of soluble reactive phosphorus concentrations , SRP, 0.7,96 µg l,1). Using five different rRNA-targeted oligonucleotide probes, net growth rates of the probe-defined bacterial groups and HNF assemblages were estimated and related to SRP using Monod kinetics, yielding growth rate constants specific for each bacterial group. We found highly significant differences among their maximum growth rates while insignificant differences were detected in the saturation constants. However, the latter constants represent only tentative estimates mainly due to insufficient sensitivity of the method used at low in situ SRP concentrations. Interestingly, in these same experiments HNF assemblages grew significantly faster than any bacterial group studied except for a small, but abundant cluster of Betaproteobacteria (targeted by the R-BT065 probe). Potential ecological implications of different growth capabilities for possible life strategies of different bacterial phylogenetic lineages are discussed. [source]

Performance Trade-offs Driven by Morphological Plasticity Contribute to Habitat Specialization of Bornean Tree Species

BIOTROPICA, Issue 4 2009
Daisy H. Dent
ABSTRACT Growth-survival trade-offs play an important role in niche differentiation of tropical tree species in relation to light-gradient partitioning. However, the mechanisms that determine differential species performance in response to light and soil resource availability are poorly understood. To examine responses to light and soil nutrient availability, we grew seedlings of five tropical tree species for 12 mo at < 2 and 18 percent full sunlight and in two soil types representing natural contrasts in nutrient availability within a lowland dipterocarp forest in North Borneo. We chose two specialists of nutrient-rich and nutrient-poor soils, respectively, and one habitat generalist. Across all species, growth was higher in high than low light and on more nutrient rich soil. Although species differed in growth rates, the ranking of species, in terms of growth, was consistent across the four treatments. Nutrient-rich soils improved seedling survival and increased growth of three species even under low light. Slower-growing species increased root allocation and reduced specific leaf area (SLA) and leaf area ratio (LAR) in response to decreased nutrient supply. All species increased LAR in response to low light. Maximum growth rates were negatively correlated with survival in the most resource-limited environment. Nutrient-poor soil specialists had low maximum growth rates but high survival at low resource availability. Specialists of nutrient-rich soils, plus the habitat generalist, had the opposite suite of traits. Fitness component trade-offs may be driven by both light and belowground resource availability. These trade-offs contribute to differentiation of tropical tree species among habitats defined by edaphic variation. [source]

Dynamics of an introduced population of mouflon Ovis aries on the sub-Antarctic archipelago of Kerguelen

ECOGRAPHY, Issue 3 2010
Renaud Kaeuffer
A commonly reported pattern in large herbivores is their propensity to irrupt and crash when colonizing new areas. However, the relative role of density-dependence, climate, and cohort effects on demographic rates in accounting for the irruptive dynamics of large herbivores remains unclear. Using a 37-yr time series of abundance in a mouflon Ovis aries population located on Haute Island, a sub-Antarctic island of Kerguelen, 1) we investigated if irruptive dynamics occurred and 2) we quantified the relative effects of density and climate on mouflon population dynamics. Being released in a new environment, we expected mouflon to show rapid growth and marked over-compensation. In support of this prediction, we found a two-phase dynamics, the first phase being characterised by an irruptive pattern best described by the , -Caughley model. Parameter estimates were rm=0.29±0.005(maximum growth rate), K=473±45 (carrying capacity) and S=2903±396 (surplus) mouflon. With a ,=3.18±0.69 our model also supported the hypothesis that density dependence is strongest at high density in large herbivores. The second phase was characterised by an unstable dynamics where growth rate was negatively affected by population abundance and winter precipitation. Climate, however, did not trigger population crashes and our model suggested that lagged density-dependence and over-grazing were the probable causes of mouflon irruptive dynamics. We compare our results with those of Soay sheep and discuss the possibility of a reversible alteration of the island carrying capacity after the initial over-grazing period. [source]

On the ecology of the rotifer Cephalodella hoodi from an extremely acidic lake

FRESHWATER BIOLOGY, Issue 9 2005
GUNTRAM WEITHOFF
Summary 1.,The biovolume-specific carbon content, relative egg volume (a measure of per-offspring reproductive investment), growth and grazing rates, and the gross growth efficiency (GGE) of the rotifer Cephalodella hoodi, isolated from an extremely acidic habitat (pH 2.65), were determined and compared with literature values for rotifers living in circum-neutral habitats in order to reveal potential special features or adaptations related to the extreme habitat of C. hoodi. 2.,Of the two dominant phytoflagellates (Ochromonas sp. and Chlamydomonas acidophila) that occur in the natural habitat of C. hoodi, only C. acidophila promoted positive growth and reproduction and, thus, the following results were obtained with C. acidophila as a food alga. 3.,The body volume-specific carbon content of C. hoodi is in the range of that found in rotifers from circum-neutral lakes, suggesting that no costly carbon investment, brought about by the thickening of the lorica, for example, was required to withstand low pH. 4.,The egg volume of C. hoodi exhibited no phenotypic plasticity dependent on the food concentration and, thus, C. hoodi allocated a constant, absolute amount of energy to each individual offspring. No adaptation to low food densities was found. 5.,A dome-shaped type II functional response curve was found to describe the ingestion of Chlamydomonas as a source of food. 6.,Compared with other rotifers, C. hoodi had a high threshold and half-saturating food concentration (=low affinity) but also a high maximum growth rate and a relatively high GGE, suggesting no severe adverse effect of low pH. [source]

Effect of Timing and Nitrogen Fertilizer Application on Winter Oilseed Rape (Brassica napus L.). I. Growth Dynamics and Seed Yield

JOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 5 2004
P. Bar
Abstract The field experiments conducted on the grey-brown podzolic soil in the four growing seasons (1998,2001) at Krzeslice Farm, central-western Poland comprised seven fertilization variants: 80NF + 80CAN; 80CAN + 80CAN; 80AN + 80AN; 80NF + 50CAN + 30CN; 80CAN + 50CAN +30CN; 80AN + 50AN + 30CN (where NF , nitrofos NPK; CAN , calcium-ammonium nitrate; AN , ammonium nitrate; CN , calcium nitrate) and control (without N) applied in split rates at the beginning of spring regrowth (80 kg N ha,1), stem elongation (80 or 50) and flower buds visible stages (30). The yielding effect of tested fertilization variants was significant in comparison with the control (2.24 t ha,1). The highest mean seed yield (3.64 t ha,1) was collected from 80AN + 80AN and 80CAN + 80CAN variants. Mean values of 4 years indicate that the second N rate division (80 + 50 + 30) decreased yield, although not significantly in comparison with these two N treatments. Plants grown on these treatments have developed different patterns of growth to yield the seeds. These patterns were characterized by very high crop growth rate during flowering (above 21 g m,2 day,1) and negative at maturation (down to ,2.5 g m,2 day,1). Plants fertilized with ammonium nitrate (80AN + 80AN) reached maximum growth rate earlier (65 days), which lasted longer (20 days) than plants fertilized with calcium-ammonium nitrate (71 days lasting 17.5 days). Plants grown on the control treatment reached the highest crop growth rate within 79 days (14.8 g m,2 day,1), which lasted 15 days. [source]

Degradation of isooctane by Mycobacterium austroafricanum IFP 2173: growth and catabolic pathway

JOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2004
F. Solano-Serena
Abstract Aims:, Isooctane (2,2,4-trimethylpentane), a major component of gasoline formulations, is recalcitrant to biodegradation probably because of the quaternary carbon group it contains. Information on the biodegradability of this hydrocarbon is essential to evaluate its fate in the environment. For these reasons, the degradation kinetics and the catabolic pathway of isooctane were investigated in Mycobacterium austroafricanum IFP 2173, the only strain characterized to use it as sole carbon and energy source. Methods and Results:, The selected strain exhibited a rather moderate maximum growth rate (,max = 0·053 h,1) but degraded isooctane up to 99% with a mineralization yield of 45%, indicating attack of the quaternary carbon group. The GC/MS identification of metabolites, 2,4,4-trimethylpentanoic and dimethylpropanoic (pivalic) acids, which transiently accumulated in the cultures indicated that degradation started from the isopropyl extremity of the molecule and subsequently proceeded by catabolism of the tert -butyl moiety. The degradation of putative metabolic intermediates was investigated. The initial isooctane oxidation system was tentatively characterized. Conclusions:, The isooctane-degrading strain harboured two candidate systems for initial alkane oxidation. Although a cytochrome P450 was induced by isooctane degradation, the functional oxidation system was probably a nonheme alkane monooxygenase as indicated by PCR amplification and RT-PCR expression of an alkB gene. Significance and Impact of the Study:, Isooctane is a recalcitrant branched alkane. A plausible pathway of its degradation by Myco. austroafricanum was put forward. [source]

Density and Water Exchange-Dependent Growth and Survival of Litopenaeus setiferus Postlarvae

JOURNAL OF THE WORLD AQUACULTURE SOCIETY, Issue 2 2001
Gabriela Palomino
This present study was designed to investigate the effects of stocking density and water exchange on the growth rate, survival and performance index of L. setiferus postlarvae under controlled laboratory conditions. The experiment was done with postlarvae (PL10 to PL40) at densities of 50, 150, 250 and 350 shrimp/m2 and various different water exchanges rate per day (0, 6, 12 and 18%). The maximum growth rate was obtained for shrimp with 12% water exchange per day at all densities. A reduction of the maximum growth rate was observed in relation to density with the highest values in shrimp stocked in a density of 50 and 150 shrimp/m2 (mean value of 0.53 mg/d) and the lowest in shrimp stocked in a density of 350 shrimp/m2 (0.24 mg/d). The multiple regression equation obtained to relate performance index (growth rate* survival : PI), shrimp density (X1) and water exchange (X2) was: PI = 0.31 + (0.001) X1+ 0.039 X2+ 2.28 × 10,6 X12+ (,0.0017) X22+ (0.000026)X1X2,R2= 0.78; P > 0.03. According to this equation the optimum shrimp density-water exchange comhination was between 5 to 12% of water exchange at stocking density of between 50 and 150 shrimp/m2. Salinity, ammonia-N and nitrite-N increased according to the time spent in tanks without water exchange. With no (0%) water exchange, water quality parameters measured were outside the optimum for L. setiferus postlarvae. The use of optimum density and water exchange in a nursery system for L. setiferus with optimum variables established is proposed. [source]

Growth in root length of the mandibular canine and premolars in a mixed-longitudinal orthodontic sample,

AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2009
Shelley L. Smith
Numerous studies of dental development focusing on eruption (clinical emergence) exist in the literature, but fewer studies examine dental development as a process extending across years or decades, and root development is commonly assessed using fractional root lengths. Here, we examine the growth of mandibular canine and premolar roots in a mixed-longitudinal sample of orthodontic patients (77 females and 74 males) from north central Texas. Multilevel models are generated for root lengths as a percentage of total tooth lengths (within films) as well as for absolute root lengths (across films). As a percentage of tooth length, roots grow with decreasing velocity through time between 7 and 14 years of age. More complex patterns appear for absolute growth in root length, with girls showing an earlier maximum growth rate for the canine than for the premolars. Substitution of dental age for chronological age reduces between-subject variation (assessed at age 11), especially for boys. A better understanding of dental maturation, including root length growth, should allow improved prediction models. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source]

Age-dependent quantitative trait loci affecting growth traits in Scottish Blackface sheep

ANIMAL GENETICS, Issue 2 2009
G. Hadjipavlou
Summary To dissect age-dependent quantitative trait loci (QTL) associated with growth and to examine changes in QTL effects over time, the Gompertz growth model was fitted to longitudinal live weight data on 788 Scottish Blackface lambs from nine half-sib families. QTL were mapped for model parameters and weekly live weights and growth rates using microsatellite markers on chromosomes 1, 2, 3, 5, 14, 18, 20 and 21. QTL significance (using , = 0.05 chromosome-wide significance thresholds, unless otherwise stated) varied with age, and those for growth rate occurred earlier than equivalent QTL for live weight. A chromosome 20 QTL for growth rate was significant from 4 to 9 weeks (maximum significance at 6 weeks) and for maximum growth rate. For live weight, this QTL was significant from 8 to 16 weeks (maximum significance at 12 weeks). A nominally significant chromosome 14 QTL was detected for growth rates from birth to week 2 in the same families and location as an 8-week weight QTL. In addition, at the same position on chromosome 14, a QTL was significant for growth rate for 17,28 weeks (maximum significance at 24 weeks). A chromosome 3 QTL was significant for weights at early ages (birth to week 4) and a growth rate QTL on chromosome 18 was significant from 8 to 12 weeks. Fitting growth curves allowed the combination of information from multiple measurements into a few biologically meaningful variables, and the detection of growth QTL that were not observed from analyses of raw weight data. These QTL describe distinct parts of an animal's growth curve trajectory, possibly enabling manipulation of this trajectory. [source]

A simple model for the determination of the relative utilization efficiency of protein by blacklip abalone (Haliotis rubra Leach)

AQUACULTURE NUTRITION, Issue 1 2010
G.A. DUNSTAN
Abstract A 6-week growth rate trial of 6.7 mm ± 1.35 SD long blacklip abalone (Haliotis rubra) fed one of four graded protein feeds (26%, 32%, 37%, 45% crude protein, CP) resulted in a maximum average growth rate of 81 ,m day,1 (percentage daily weight gain of 5.2% day,1) with the 45% CP diet. Based on the results, a new, simple, non-destructive method to calculate the relative utilization efficiencies (RUE) of nutrients is presented to estimate the relative contributions of a nutrient to growth, body maintenance and the excess used for energy. Calculations of RUE of protein estimated that at the maximum growth rate, 59% of the CP was responsible for growth, while 31% was used for body maintenance and an excess of 10% was lost and presumably catabolized for energy and carbohydrate anabolism. At the %CP where the highest proportion of CP was used for growth, i.e. the maximum RUE of protein for growth (slightly higher at 62%), 35% was used for body maintenance and only 3% of the excess was lost to energy. [source]

Complex responses to culture conditions in Pseudomonas syringae pv. tomato DC3000 continuous cultures: The role of iron in cell growth and virulence factor induction

BIOTECHNOLOGY & BIOENGINEERING, Issue 5 2010
Beum Jun Kim
Abstract The growth of a model plant pathogen, Pseudomonas syringae pv. tomato DC3000, was investigated using a chemostat culture system to examine environmentally regulated responses. Using minimal medium with iron as the limiting nutrient, four different types of responses were obtained in a customized continuous culture system: (1) stable steady state, (2) damped oscillation, (3) normal washout due to high dilution rates exceeding the maximum growth rate, and (4) washout at low dilution rates due to negative growth rates. The type of response was determined by a combination of initial cell mass and dilution rate. Stable steady states were obtained with dilution rates ranging from 0.059 to 0.086,h,1 with an initial cell mass of less than 0.6,OD600. Damped oscillations and negative growth rates are unusual observations for bacterial systems. We have observed these responses at values of initial cell mass of 0.9,OD600 or higher, or at low dilution rates (<0.05,h,1) irrespectively of initial cell mass. This response suggests complex dynamics including the possibility of multiple steady states. Iron, which was reported earlier as a growth limiting nutrient in a widely used minimal medium, enhances both growth and virulence factor induction in iron-supplemented cultures compared to unsupplemented controls. Intracellular iron concentration is correlated to the early induction (6,h) of virulence factors in both batch and chemostat cultures. A reduction in aconitase activity (a TCA cycle enzyme) and ATP levels in iron-limited chemostat cultures was observed compared to iron-supplemented chemostat cultures, indicating that iron affects central metabolic pathways. We conclude that DC3000 cultures are particularly dependent on the environment and iron is likely a key nutrient in determining physiology. Biotechnol. Bioeng. 2010;105: 955,964. © 2009 Wiley Periodicals, Inc. [source]

Respirometric evaluation and modeling of glucose utilization by Escherichia coli under aerobic and mesophilic cultivation conditions

BIOTECHNOLOGY & BIOENGINEERING, Issue 1 2007
G. Insel
Abstract The study presents a mechanistic model for the evaluation of glucose utilization by Escherichia coli under aerobic and mesophilic growth conditions. In the first step, the experimental data was derived from batch respirometric experiments conducted at 37°C, using two different initial substrate to microorganism (S0/X0) ratios of 15.0 and 1.3 mgCOD/mgSS. Acetate generation, glycogen formation and oxygen uptake rate profile were monitored together with glucose uptake and biomass increase throughout the experiments. The oxygen uptake rate (OUR) exhibited a typical profile accounting for growth on glucose, acetate and glycogen. No acetate formation (overflow) was detected at low initial S0/X0 ratio. In the second step, the effect of culture history developed under long-term growth limiting conditions on the kinetics of glucose utilization by the same culture was evaluated in a sequencing batch reactor (SBR). The system was operated at cyclic steady state with a constant mean cell residence time of 5 days. The kinetic response of E.coli culture was followed by similar measurements within a complete cycle. Model calibration for the SBR system showed that E. coli culture regulated its growth metabolism by decreasing the maximum growth rate (lower ) together with an increase of substrate affinity (lower KS) as compared to uncontrolled growth conditions. The continuous low rate operation of SBR system induced a significant biochemical substrate storage capability as glycogen in parallel to growth, which persisted throughout the operation. The acetate overflow was observed again as an important mechanism to be accounted for in the evaluation of process kinetics. Biotechnol. Bioeng. 2007;96: 94,105. © 2006 Wiley Periodicals, Inc. [source]

A new approach for modelling simultaneous storage and growth processes for activated sludge systems under aerobic conditions

BIOTECHNOLOGY & BIOENGINEERING, Issue 5 2005
Gürkan Sin
Abstract By critically evaluating previous models, a new mechanistic model is developed to describe simultaneous storage and growth processes occurring in activated sludge systems under aerobic conditions. Identifiability was considered an important criterion during the model development since it among others helps to increase the realiability and applicability of models to full-scale WWTPs. A second order model was proposed for description of the degradation of the storage products under famine conditions. The model is successfully calibrated by only using OUR data obtained from batch experiments. Calibrations were performed with biomass from full-scale WWTPs in Belgium and Spain. Predictions of the calibrated model were successfully confirmed using off-line PHB measurements, supporting the validity of the model. An iterative experimental design procedure was successfully applied and found to remarkably improve the parameter estimation accuracy for the growth on storage parameters K1 and K2, which used to have large confidence intervals when using standard experiments. The estimated biomass growth yield on substrate (0.58 mgCOD/mgCOD) is quite close to the theoretically expected range for heterotrophic growth. This became possible by properly accounting for the storage process. Moreover, the maximum growth rate was predicted in the range 0.7,1.3 per day. This range, albeit quite lower than the values reported for the growth-based ASM models, is believed to be more realistic. Finally, the new model is expected to better and more mechanistically describe simultaneous storage and growth activities of activated sludge systems and as such could contribute to improved design, operation and control of those systems. © 2005 Wiley Periodicals, inc. [source]

Role of nutrient supply on cell growth in bioreactor design for tissue engineering of hematopoietic cells

BIOTECHNOLOGY & BIOENGINEERING, Issue 7 2005
Pragyansri Pathi
Abstract In the present study, a dynamic mathematical model for the growth of granulocyte progenitor cells in the hematopoietic process is developed based on the principles of diffusion and chemical reaction. This model simulates granulocyte progenitor cell growth and oxygen consumption in a three-dimensional (3-D) perfusion bioreactor. Material balances on cells are coupled to the nutrient balances in 3-D matrices to determine the effects of transport limitations on cell growth. The method of volume averaging is used to formulate the material balances for the cells and the nutrients in the porous matrix containing the cells. All model parameters are obtained from the literature. The maximum cell volume fraction reached when oxygen is depleted in the cell layer at 15 days and is nearly 0.63, corresponding to a cell density of 2.25 × 108 cells/mL. The substrate inhibition kinetics for cell growth lead to complex effects with respect to the roles of oxygen concentration and supply by convection and diffusion on cell growth. Variation in the height of the liquid layer above the cell matrix where nutrient supply is introduced affected the relative and absolute amounts of oxygen supply by hydrodynamic flow and by diffusion across a gas permeable FEP membrane. Mass transfer restrictions of the FEP membrane are considerable, and the supply of oxygen by convection is essential to achieve higher levels of cell growth. A maximum growth rate occurs at a specific flow rate. For flow rates higher than this optimal, the high oxygen concentration led to growth inhibition and for lower flow rates growth limitations occur due to insufficient oxygen supply. Because of the nonlinear effects of the autocatalytic substrate inhibition growth kinetics coupled to the convective transport, the rate of growth at this optimal flow rate is higher than that in a corresponding well-mixed reactor where oxygen concentration is set at the maximum indicated by the inhibitory kinetics. ©2005 Wiley Periodicals, Inc. [source]

Maximum growth rates and possible life strategies of different bacterioplankton groups in relation to phosphorus availability in a freshwater reservoir

Evaluation of the fermentability of oat fractions obtained by debranning using lactic acid bacteria

JOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2008
G. Kedia
Abstract Aims:, The overall kinetics of the fermentation of four oat fractions obtained by debranning using three potentially probiotic lactic acid bacteria were investigated. The main objective was to study the suitability of these fractions as fermentation media for the growth and the metabolic production of bacteria isolated from human intestine. Methods and Results:, The cell growth, lactic acid production and substrate uptakes of the three lactobacilli was monitored for 30 h. An unstructured mathematical model was used to describe and fit the experimental data. In the medium from fraction B (1,3% pearlings or ,-glucan-rich fraction) all strains reached the highest cell populations, maximum growth rates and maximum lactic acid productions. This could be because of the high levels of total fibre and ,-glucan of this fraction. Limited growth and lactic acid formation was found in medium A (0,1% pearlings or bran-rich fraction). Conclusions:, Medium B (1,3% pearling fraction) is the most suitable for fermentation and produces considerably higher probiotic cell concentrations. Significance and Impact of the Study:, Debranning technology could be used to separate fractions from cereal grains for the production of functional formulations with higher probiotic levels than the ones that were obtained with the whole grain. [source]

Hypoxia enhances proliferation of mouse embryonic stem cell-derived neural stem cells

BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2010
Carlos A.V. Rodrigues
Abstract Neural stem (NS) cells can provide a source of material with potential applications for neural drug testing, developmental studies, or novel treatments for neurodegenerative diseases. Herein, the ex vivo expansion of a model system of mouse embryonic stem (mES) cell-derived NS cells was characterized and optimized, cells being cultivated under adherent conditions. Culture was first optimized in terms of initial cell plating density and oxygen concentration, known to strongly influence brain-derived NS cells. To this end, the growth of cells cultured under hypoxic (2%, 5%, and 10% O2) and normoxic (20% O2) conditions was compared. The results showed that 2,5% oxygen, without affecting multipotency, led to fold increase values in total cell number about twice higher than observed under 20% oxygen (20-fold vs. 10-fold, respectively) this effect being more pronounced when cells were plated at low density. With an optimal cell density of 104,cells/cm2, the maximum growth rates were 1.9,day,1 under hypoxia versus 1.7,day,1 under normoxia. Cell division kinetics analysis by flow cytometry based on PKH67 tracking showed that when cultured in hypoxia, cells are at least one divisional generation ahead compared to normoxia. In terms of cell cycle, a larger population in a quiescent G0 phase was observed in normoxic conditions. The optimization of NS cell culture performed here represents an important step toward the generation of a large number of neural cells from a reduced initial population, envisaging the potential application of these cells in multiple settings. Biotechnol. Bioeng. 2010;106: 260,270. © 2009 Wiley Periodicals, Inc. [source]