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1.
Two equations, describing surface colonization, were evaluated and compared using suspended glass slides in a continuous culture ofPseudomonas aeruginosa. These equations were used to determine surface growth rates from the number and distribution of cells present on the surface after incubation. One of these was the colonization equation which accounts for simultaneous attachment and growth of bacteria on surfaces: $$N = (A/\mu )e^{\mu t} - A/\mu $$ where N=number of cells on surface (cells field?1); A=attachment rate (cells field?1h?1);μ=specific growth rate (h?1); t=incubation period (h). The other was the surface growth rate equation which assumes that the number of colonies of a given size (Ci) will reach a constant value (Cmax) which is equal to A divided byμ: $$\mu = \frac{{\ln \left( {\frac{N}{{C_i }} + 1} \right)}}{t}$$ Both equations gave similar results and the time required to approximate Cmax may not be as long as was previously thought. In all cases both A andμ continuously decreased throughout the incubation period. These decreases may be due to various effects of microbial accumulation on the surface. Both equations accurately determined surface growth rates despite highly variable attachment rates. Growth rates were similar for both the liquid phase of the culture and the solid-liquid interface (0.4 h?1). Use of the surface growth rate equation is favored over the use of the colonization equation since the former does not require a computer to solve forμ and the counting procedure is simplified. 相似文献
2.
A surface growth rate equation is derived which describes simultaneous growth and attachment during microbial surface colonization. The equation simplifies determination of attachment and growth rate, and does not require a computer program for solution. This rate equation gives the specific growth rate (Μ) as a function of the number of cells on the surface (N), the incubation period (t), and the number of colonies (Ci) containing either one cell, two cells, four cells, etc, as shown below. $$\mu = \frac{{\ln (\frac{N}{{C_i }} + 1)}}{t}$$ The attachment rate (A) is given by the following relationship: $$A = \mu C_i $$ The proposed colonization kinetics are compared with exponential growth kinetics using 3-dimensional computer plots. Colonization kinetics diverged most from exponential kinetics when the growth rate was low or the attachment rate was high. Using these kinetics, it is possible to isolate the effects of growth and attachment on microbial surface colonization. 相似文献
3.
4.
Joseph R. Stinziano Patrick B. Morgan Douglas J. Lynch Aaron J. Saathoff Dayle K. McDermitt David T. Hanson 《Plant, cell & environment》2017,40(8):1256-1262
Phenotyping for photosynthetic gas exchange parameters is limiting our ability to select plants for enhanced photosynthetic carbon gain and to assess plant function in current and future natural environments. This is due, in part, to the time required to generate estimates of the maximum rate of ribulose‐1,5‐bisphosphate carboxylase oxygenase (Rubisco) carboxylation (Vc,max) and the maximal rate of electron transport (Jmax) from the response of photosynthesis (A) to the CO2 concentration inside leaf air spaces (Ci). To relieve this bottleneck, we developed a method for rapid photosynthetic carbon assimilation CO2 responses [rapid A–Ci response (RACiR)] utilizing non‐steady‐state measurements of gas exchange. Using high temporal resolution measurements under rapidly changing CO2 concentrations, we show that RACiR techniques can obtain measures of Vc,max and Jmax in ~5 min, and possibly even faster. This is a small fraction of the time required for even the most advanced gas exchange instrumentation. The RACiR technique, owing to its increased throughput, will allow for more rapid screening of crops, mutants and populations of plants in natural environments, bringing gas exchange into the phenomic era. 相似文献
5.
Evaluation of a proposed surface colonization equation usingThermothrix thiopara as a model organism
The colonization equation shown below was evaluated usingThermothrix thiopara as a model organism. $$N = (A/\mu )e^{\mu t} - A/\mu $$ where: N=number of cells on surface (cells field?1); A = attachment rate (cells field?1 h?1); M=specific growth rate (h?1); t=incubation period (h). Previous studies of microbial surface colonization consider attachment and growth independently. However, the proposed colonization equation integrates the effects of simultaneous attachment and growth. Using this equation, the specific growth rate ofT. thiopara was found to be 0.38±0.3 h?1 during in situ colonization. Estimates ofμ were independent of incubation period after 4 h (2 generations). Shorter incubations were inadequate to produce sufficient microcolonies for accurate determination of specific growth rate. Empirical data for the time course of colonization fell within the 95% confidence interval of predicted values. The attachment rate, although assumed to be constant, was found to continuously increase with time. This increase may have been an artifact due to the continuous deposition of travertine on the surface, or may indicate the need for a function to replace A in the colonization equation. Using the exponential growth equation, the progeny of cells that attach during incubation are considered to be progeny of cells that attach initially. This erroneously inflated the growth rate by 55%. 相似文献
6.
Energization and activation of inorganic carbon uptake by light in cyanobacteria 总被引:11,自引:3,他引:8
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The requirement of the inorganic carbon (Ci) transport system for light in cyanobacteria was investigated in Anabaena variabilis by the filtering centrifugation technique and in a mutant (E1) isolated from Anacystis nidulans using a gas exchange system. Ci transport capability increased with time of preillumination and decreased following darkening. Full activity could not be obtained by operating either photosystem II (PSII) or photosystem I alone. 3(3,4 Dichlorophenyl)-1,1 dimethylurea strongly inhibited Ci uptake. Very low activity of PSII was sufficient to activate Ci uptake. However, in the presence of dithiothreitol PSII activity was not required. We conclude that light may be required to activate as well as to energize Ci uptake in cyanobacteria. 相似文献
7.
Gracilaria tenuistipitata Zhang et Xia was cultured for 15 d at low, normal and high inorganic carbon concentrations under constant light, temperature and nutrient conditons. Carbonic anhydrase (CA; EC 4.2.1.1.) activity, ribulose-1,5-bisphosphate carboxylase/ oxygenase (Rubisco; EC 4.1.1.39) content, pigment content and C/N ratio were measured, and also the photosynthesis and growth rates. Both Rubisco content and CA activity increased under conditions of low inorganic carbon (Ci) but decreased at high Ci with respect to the control. The amount of pigments declined considerably at high Ci and was slightly higher at low Ci. The maximum rate of photosynthesis and the photosynthetic efficiency increased in low Ci and the opposite was found at high Ci concentration. The effects of Ci concentration on maximum rate of photosynthesis and photosynthetic efficiency are discussed in relation to the variation in pigment and Rubisco contents and CA activity. The data indicate that Ci may be an important factor controlling the photosynthetic physiology of G. tenuistipitata with regard, not only to the enzymes of Ci metabolism, but also to the pigment content.Abbreviations APSmax
maximum apparent photosynthetic rate
- CA
carbonic anhydrase
- Chl
chlorophyll
- Ci
inorganic carbon
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase
This work has been supported by grants No. PB91-0962 and No. MAR90-0365 from Spanish Direction for Science and Technology (DIGICYT). M.J. G-S holds a fellowship from the DIGICYT. 相似文献
8.
Makoto Watanabe Yu Kamimaki Marino Mori Shigeaki Okabe Izumi Arakawa Yoshiyuki Kinose Satoshi Nakaba Takeshi Izuta 《Journal of plant research》2018,131(6):907-914
Ozone is an air pollutant that negatively affects photosynthesis in woody plants. Previous studies suggested that ozone-induced reduction in photosynthetic rates is mainly attributable to a decrease of maximum carboxylation rate (Vcmax) and/or maximum electron transport rate (Jmax) estimated from response of net photosynthetic rate (A) to intercellular CO2 concentration (Ci) (A/Ci curve) assuming that mesophyll conductance for CO2 diffusion (gm) is infinite. Although it is known that Ci-based Vcmax and Jmax are potentially influenced by gm, its contribution to ozone responses in Ci-based Vcmax and Jmax is still unclear. In the present study, therefore, we analysed photosynthetic processes including gm in leaves of Siebold’s beech (Fagus crenata) seedlings grown under three levels of ozone (charcoal-filtered air or ozone at 1.0- or 1.5-times ambient concentration) for two growing seasons in 2016–2017. Leaf gas exchange and chlorophyll fluorescence were simultaneously measured in July and September of the second growing season. We determined the A, stomatal conductance to water vapor and gm, and analysed A/Ci curve and A/Cc curve (Cc: chloroplast CO2 concentration). We also determined the Rubisco and chlorophyll contents in leaves. In September, ozone significantly decreased Ci-based Vcmax. At the same time, ozone decreased gm, whereas there was no significant effect of ozone on Cc-based Vcmax or the contents of Rubisco and chlorophyll in leaves. These results suggest that ozone-induced reduction in Ci-based Vcmax is a result of the decrease in gm rather than in carboxylation capacity. The decrease in gm by elevated ozone was offset by an increase in Ci, and Cc did not differ depending on ozone treatment. Since Cc-based Vcmax was also similar, A was not changed by elevated ozone. We conclude that gm is an important factor for reduction in Ci-based Vcmax of Siebold’s beech under elevated ozone. 相似文献
9.
Bunce JA 《Photosynthesis research》2000,63(1):59-67
To determine how parameters of a Farquhar-type photosynthesis model varied with measurement temperature and with growth temperature, eight cool and warm climate herbaceous crop and weed species were grown at 15 and 25 °C and single leaf carbon dioxide and water vapor exchange rates were measured over the range of 15 – 35 °C. Photosynthetic parameters examined were the initial slope of the response of assimilation rate (A) to substomatal carbon dioxide concentration (Ci), A at high Ci, and stomatal conductance. The first two measurements allow calculation of VCmax, the maximum rate of carboxylation of ribulose bisphosphate carboxylase and Jmax, the maximum rate of photosynthetic electron transport, of Farquhar-type photosynthesis models. In all species, stomatal conductance increased exponentially with temperature over the whole range of 15 – 35 °C, even when A decreased at high measurement temperature. There were larger increases in conductance over this temperature range in the warm climate species (4.3 ×) than in the cool climate species (2.5 ×). The initial slope of A vs. Ci exhibited an optimum temperature which ranged from 20 to 30 °C. There was a larger increase in the optimum temperature of the initial slope at the warmer growth temperature in the cool climate species than in the warm climate species. The optimum temperature for A at high Ci ranged from 25 to 30 °C among species, but changed little with growth temperature. The absolute values of both the initial slope of A vs. Ci and A at high Ci were increased about 10% by growth at the warmer temperature in the warm climate species, and decreased about 20% in the cool climate species. The ratio of Jmax — VCmax normalized to 20 °C varied by more than a factor of 2 across species and growth temperatures, but differences in the temperature response of photosynthesis were more related to variation in the temperature dependencies of Jmax and VCmax than to the ratio of their normalized values.This revised version was published online in October 2005 with corrections to the Cover Date. 相似文献
10.
The parameters estimated from traditional A/C
i curve analysis are dependent upon some underlying assumptions that substomatal CO2 concentration (C
i) equals the chloroplast CO2 concentration (C
c) and the C
i value at which the A/C
i curve switches between Rubisco- and electron transport-limited portions of the curve (C
i-t) is set to a constant. However, the assumptions reduced the accuracy of parameter estimation significantly without taking
the influence of C
i-t value and mesophyll conductance (g
m) on parameters into account. Based on the analysis of Larix gmelinii’s A/C
i curves, it showed the C
i-t value varied significantly, ranging from 24 Pa to 72 Pa and averaging 38 Pa. t-test demonstrated there were significant differences in parameters respectively estimated from A/C
i and A/C
c curve analysis (p<0.01). Compared with the maximum ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) carboxylation rate (Vcmax), the maximum electron transport rate (Jmax) and Jmax/Vcmax estimated from A/C
c curve analysis which considers the effects of g
m limit and simultaneously fits parameters with the whole A/C
c curve, mean Vcmax estimated from A/C
i curve analysis (Vcmax-C
i) was underestimated by 37.49%; mean Jmax estimated from A/C
i curve analysis (Jmax-C
i) was overestimated by 17.8% and (Jmax-C
i)/(Vcmax-C
i) was overestimated by 24.2%. However, there was a significant linear relationship between Vcmax estimated from A/C
i curve analysis and Vcmax estimated from A/C
c curve analysis, so was it Jmax (p<0.05). 相似文献
11.
Acclimation to rapidly fluctuating light, simulating shallow aquatic habitats, is altered depending on inorganic carbon (Ci) availability. Under steady light of 50 μmol photons·m?2·s?1, the growth rate of Synechococcus elongatus PCC7942 was similar in cells grown in high Ci (4 mM) and low Ci (0.02 mM), with induced carbon concentrating mechanisms compensating for low Ci. Growth under fluctuating light of a 1‐s period averaging 50 μmol photons·m?2·s?1 caused a drop in growth rate of 28%±6% in high Ci cells and 38%±8% in low Ci cells. In high Ci cells under fluctuating light, the PSI/PSII ratio increased, the PSII absorption cross‐section decreased, and the PSII turnover rate increased in a pattern similar to high‐light acclimation. In low Ci cells under fluctuating light, the PSI/PSII ratio decreased, the PSII absorption cross‐section decreased, and the PSII turnover remained slow. Electron transport rate was similar in high and low Ci cells but in both was lower under fluctuating than under steady light. After acclimation to a 1‐s period fluctuating light, electron transport rate decreased under steady or long‐period fluctuating light. We hypothesize that high Ci cells acclimated to exploit the bright phases of the fluctuating light, whereas low Ci cells enlarged their PSII pool to integrate the fluctuating light and dampen the variation of the electron flux into a rate‐restricted Ci pool. Light response curves measured under steady light, widely used to predict photosynthetic rates, do not properly predict photosynthetic rates achieved under fluctuating light, and exploitation of fluctuating light is altered by Ci status. 相似文献
12.
The role of external carbonic anhydrase in photosynthesis during growth of the marine diatom Chaetoceros muelleri
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Tamsyne Jade Smith‐Harding John Beardall James Gordon Mitchell 《Journal of phycology》2017,53(6):1159-1170
Carbon dioxide concentrating mechanisms (CCMs) act to improve the supply of CO2 at the active site of ribulose‐1,5‐bisphosphate carboxylase/oxygenase. There is substantial evidence that in some microalgal species CCMs involve an external carbonic anhydrase (CAext) and that CAext activity is induced by low CO2 concentrations in the growth medium. However, much of this work has been conducted on cells adapted to air‐equilibrium concentrations of CO2, rather than to changing CO2 conditions caused by growing microalgal populations. We investigated the role of CAext in inorganic carbon (Ci) acquisition and photosynthesis at three sampling points during the growth cycle of the cosmopolitan marine diatom Chaetoceros muelleri. We observed that CAext activity increased with decreasing Ci, particularly CO2, concentration, supporting the idea that CAext is modulated by external CO2 concentration. Additionally, we found that the contribution of CAext activity to carbon acquisition for photosynthesis varies over time, increasing between the first and second sampling points before decreasing at the last sampling point, where external pH was high. Lastly, decreases in maximum quantum yield of photosystem II (Fv/Fm), chlorophyll, maximum relative electron transport rate, light harvesting efficiency (α) and maximum rates of Ci‐ saturated photosynthesis (Vmax) were observed over time. Despite this decrease in photosynthetic capacity an up‐regulation of CCM activity, indicated by a decreasing half‐saturation constant for CO2 (K0.5CO2), occurred over time. The flexibility of the CCM during the course of growth in C. muelleri may contribute to the reported dominance and persistence of this species in phytoplankton blooms. 相似文献
13.
Elly Spijkerman 《Journal of phycology》2010,46(4):658-664
Inorganic phosphorus (Pi) and carbon (here, CO2) potentially limit the photosynthesis of phytoplankton simultaneously (colimitation). A single Pi limitation generally reduces photosynthesis, but the effect of a colimitation is not known. Therefore, photosynthesis was measured under Pi‐limited conditions and high and low CO2, and osmo‐mixotrophic (i.e., growth in the presence of glucose) conditions that result in colimiting conditions in some cases. The green alga Chlamydomonas acidophila Negoro was used as a model organism because low Pi and CO2 concentrations likely influence its photosynthetic rates in its natural environment. Results showed a decreasing maximum photosynthetic rate (Pmax) and maximum quantum yield (ΦII) with increasing Pi limitation. In addition, a Pi limitation enhanced the relative contribution of dark respiration to Pmax (Rd:Pmax) but did not influence the compensation light intensity. Pmax positively correlated with the cellular RUBISCO content. Osmo‐mixotrophic conditions resulted in similar Pmax, ΦII, and RUBISCO content as in high‐CO2 cultures. The low‐CO2 cultures were colimited by Pi and CO2 and had the highest Pmax, ΦII, and RUBISCO content. Colimiting conditions for Pi and CO2 in C. acidophila resulted in an enhanced mismatch between photosynthesis and growth rates compared to the effect of a single Pi limitation. Primary productivity of colimited phytoplankton could thus be misinterpreted. 相似文献
14.
A chloroplast pump model for the CO2 concentrating mechanism in the diatom Phaeodactylum tricornutum
Brian M. Hopkinson 《Photosynthesis research》2014,121(2-3):223-233
Prior analysis of inorganic carbon (Ci) fluxes in the diatom Phaeodactylum tricornutum has indicated that transport of Ci into the chloroplast from the cytoplasm is the major Ci flux in the cell and the primary driving force for the CO2 concentrating mechanism (CCM). This flux drives the accumulation of Ci in the chloroplast stroma and generates a CO2 deficit in the cytoplasm, inducing CO2 influx into the cell. Here, the “chloroplast pump” model of the CCM in P. tricornutum is formalized and its consistency with data on CO2 and HCO3 ? uptake rates, carbonic anhydrase (CA) activity, intracellular Ci concentration, intracellular pH, and RubisCO characteristics is assessed. The chloroplast pump model can account for the major features of the data. Analysis of photosynthetic and Ci uptake rates as a function of external Ci concentration shows that the model has the most difficulty obtaining sufficiently low cytoplasmic CO2 concentrations to support observed CO2 uptake rates at low external Ci concentrations and achieving high rates of photosynthesis. There are multiple ways in which model parameters can be varied, within a plausible range, to match measured rates of photosynthesis and CO2 uptake. To increase CO2 uptake rates, CA activity can be increased, kinetic characteristics of the putative chloroplast pump can be enhanced to increase HCO3 ? export, or the cytoplasmic pH can be raised. To increase the photosynthetic rate, the permeability of the pyrenoid to CO2 can be reduced or RubisCO content can be increased. 相似文献
15.
V. P. Venugopalan M. Kuehn M. Hausner D. Springael P. A. Wilderer S. Wuertz 《Applied microbiology》2005,71(5):2677-2686
The architecture of a Sphingomonas biofilm was studied during early phases of its formation, using strain L138, a gfp-tagged derivative of Sphingomonas sp. strain LB126, as a model organism and flow cells and confocal laser scanning microscopy as experimental tools. Spatial and temporal distribution of cells and exopolymer secretions (EPS) within the biofilm, development of microcolonies under flow conditions representing varied Reynolds numbers, and changes in diffusion length with reference to EPS production were studied by sequential sacrificing of biofilms grown in multichannel flow cells and by time-lapse confocal imaging. The area of biofilm in terms of microscopic images required to ensure representative sampling varied by an order of magnitude when area of cell coverage (2 × 105 μm2) or microcolony size (1 × 106 μm2) was the biofilm parameter under investigation. Hence, it is necessary to establish the inherent variability of any biofilm metric one is attempting to quantify. Sphingomonas sp. strain L138 biofilm architecture consisted of microcolonies and extensive water channels. Biomass and EPS distribution were maximal at 8 to 9 μm above the substratum, with a high void fraction near the substratum. Time-lapse confocal imaging and digital image analysis showed that growth of the microcolonies was not uniform: adjacently located colonies registered significant growth or no growth at all. Microcolonies in the biofilm had the ability to move across the attachment surface as a unit, irrespective of fluid flow direction, indicating that movement of microcolonies is an inherent property of the biofilm. Width of water channels decreased as EPS production increased, resulting in increased diffusion distances in the biofilm. Changing hydrodynamic conditions (Reynolds numbers of 0.07, 52, and 87) had no discernible influence on the characteristics of microcolonies (size, shape, or orientation with respect to flow) during the first 24 h of biofilm development. Inherent factors appear to have overriding influence, vis-à-vis environmental factors, on early stages of microcolony development under these laminar flow conditions. 相似文献
16.
The effect of sodium chloride and triadimefon (TDM) on the chlorophyll (Chl) content, net photosynthetic rates (PN), rate of transpiration (E), and intercellular CO2 concentration (Ci) in Raphanus sativus was studied. The effect of NaCl salinity was partially ameliorated by TDM which caused increase in Chl content, PN, and Ci. TDM also increased root dry matter production, decreased E, and increased the water use efficiency. 相似文献
17.
Application of the widely used Farquhar model of photosynthesis in interpretation of gas exchange data assumes that photosynthetic properties are homogeneous throughout the leaf. Previous studies showed that heterogeneity in stomatal conductance (gs) across a leaf could affect the shape of the measured leaf photosynthetic CO2 uptake rate (A) versus intercellular CO2 concentration (Ci) response curve and, in turn, estimation of the critical biochemical parameters of this model. These are the maximum rates of carboxylation (Vc,max), whole-chain electron transport (Jmax), and triose-P utilization (VTPU). The effects of spatial variation in Vc,max, Jmax, and VTPU on estimation of leaf averages of these parameters from A-Ci curves measured on a whole leaf have not been investigated. A mathematical model incorporating defined degrees of spatial variability in Vc,max and Jmax was constructed. One hundred and ten theoretical leaves were simulated, each with the same average Vc,max and Jmax, but different coefficients of variation of the mean (CVVJ) and varying correlation between Vc,max and Jmax (Ω). Additionally, the interaction of variation in Vc,max and Jmax with heterogeneity in VTPU, gs, and light gradients within the leaf was also investigated. Transition from Vc,max- to Jmax-limited photosynthesis in the A-Ci curve was smooth in the most heterogeneous leaves, in contrast to a distinct inflection in the absence of heterogeneity. Spatial variability had little effect on the accuracy of estimation of Vc,max and Jmax from A-Ci curves when the two varied in concert (Ω = 1.0), but resulted in underestimation of both parameters when they varied independently (up to 12.5% in Vc,max and 17.7% in Jmax at CVVJ = 50%; Ω = 0.3). Heterogeneity in VTPU also significantly affected parameter estimates, but effects of heterogeneity in gs or light gradients were comparatively small. If Vc,max and Jmax derived from such heterogeneous leaves are used in models to project leaf photosynthesis, actual A is overestimated by up to 12% at the transition between Vc,max- and Jmax-limited photosynthesis. This could have implications for both crop production and Earth system models, including projections of the effects of atmospheric change. 相似文献
18.
We studied growth and photosynthesis of cucumber (Cucumis sativus) seedlings under two vapor-pressure deficit levels (VPD; 0.4 and 3.0 kPa), two salinity levels (0 mM and 34 mM NaCl), and two CO2 concentrations ([CO2]; 400 and 1,000 μmol mol–1). Relative growth rate (RGR) decreased with increasing VPD, but the causal factor differed between salinity levels and CO2 concentrations. Under ambient [CO2], RGR decreased with increasing VPD at low salinity mainly due to decreased leaf area ratio (LAR), and decreased net assimilation rate (NAR) at high salinity. The decrease in intercellular [CO2] (Ci) with decreasing stomatal conductance caused by high VPD did not significantly limit net photosynthetic rate (PN) at low salinity, but PN was potentially limited by Ci at high salinity. At high [CO2], high VPD reduced LAR, but did not affect NAR. This is because the decrease in Ci occurred where slope of PN–Ci curve was almost flat. 相似文献
19.
Evidence for Inorganic Carbon Transport by Intact Chloroplasts of Chlamydomonas reinhardtii 总被引:19,自引:15,他引:4
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Isolated intact chloroplasts from wall-less mutants of Chlamydomonas reinhardtii accumulate inorganic carbon (Ci) from the medium provided the cells had been adapted to low CO2 photoautotrophic growth conditions. Chloroplasts from cultures grown on high (5%) CO2 or photoheterotrophically with acetate did not accumulate inorganic carbon. Chloroplast Ci accumulation from low CO2 grown cells was light dependent and was inhibited by uncouplers and inhibitors of electron transport. In a model for Ci accumulation by Chlamydomonas, it is proposed that CO2 diffuses into the cell and Ci accumulation occurs in the chloroplast. 相似文献
20.
Lab and pilot scale batch cultivations of a CHO K1/dhfr? host cell line were conducted to evaluate on‐line multifrequency permittivity measurements as a process monitoring tool. The β‐dispersion parameters such as the characteristic frequency (fC) and the permittivity increment (Δεmax) were calculated on‐line from the permittivity spectra. The dual‐frequency permittivity signal correlated well with the off‐line measured biovolume and the viable cell density. A significant drop in permittivity was monitored at the transition from exponential growth to a phase with reduced growth rate. Although not reflected in off‐line biovolume measurements, this decrease coincided with a drop in OUR and was probably caused by the depletion of glutamine and a metabolic shift occurring at the same time. Sudden changes in cell density, cell size, viability, capacitance per membrane area (CM), and effects caused by medium conductivity (σm) could be excluded as reasons for the decrease in permittivity. After analysis of the process data, a drop in fC as a result of a fall in intracellular conductivity (σi) was identified as responsible for the observed changes in the dual‐frequency permittivity signal. It is hypothesized that the β‐dispersion parameter fC is indicative of changes in nutrient availability that have an impact on intracellular conductivity σi. On‐line permittivity measurements consequently not only reflect the biovolume but also the physiological state of mammalian cell cultures. These findings should pave the way for a better understanding of the intracellular state of cells and render permittivity measurements an important tool in process development and control. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2010 相似文献