Showing papers on "Chemostat published in 1991"
TL;DR: Methods of cell culture which enable the control of specific growth rate and expression of iron-regulated membrane proteins within Gram-negative biofilms were employed for various clinical isolates of Pseudomonas aeruginosa taken from the sputum of cystic fibrosis patients and of a laboratory strain of Escherichia coli to assess susceptibility towards ciprofloxacin.
Abstract: Methods of cell culture which enable the control of specific growth rate and expression of iron-regulated membrane proteins within Gram-negative biofilms were employed for various clinical isolates of Pseudomonas aeruginosa taken from the sputum of cystic fibrosis patients and of a laboratory strain of Escherichia coli. Susceptibility towards ciprofloxacin was assessed as a function of growth-rate for intact biofilms, cells resuspended from the biofilms and also for newly formed daughter cells shed from the biofilm during its growth and development. Patterns of susceptibility with growth rate were compared to those of suspended cultures grown in a chemostat. In all instances the susceptibility of chemostat cultures was directly related to growth rate. Whilst little difference was observed in the susceptibility pattern for P. aeruginosa strains with different observed levels of mucoidness, such populations were generally more susceptible towards ciprofloxacin than those of E. coli. At fast rates of growth P. aeruginosa cells resuspended from biofilms were significantly more resistant than chemostat grown cells. Intact P. aeruginosa biofilms were significantly more resistant than cells resuspended from them. This is in contrast to E. coli, where cells resuspended from biofilm and intact biofilms were, at the slower rates of growth, equivalent and significantly more susceptible than chemostat-grown cells. At high growth rates all methods of E. coli culture produced cells of equivalent susceptibility. For all strains, daughter cells dislodged from the biofilms demonstrated a high level of susceptibility towards ciprofloxacin which was unaffected by growth rate. This sensitivity corresponded to that of the fastest grown cells in the chemostat.
245 citations
TL;DR: It is concluded that in the psychrotrophic strain P. fluorescens MF0, growth temperature exerts a specific control upon the activity of certain enzymes, probably different from a cold shock or heat shock response.
Abstract: In accordance with previous results, the activity of extracellular proteases from Pseudomonas fluorescens MF0 is maximal at a growth temperature of 17.5 degrees C, well below the optimal growth temperature. In addition, the activities of three periplasmic phosphatases display the same growth temperature optimum. Chemostat experiments have shown that it is the growth temperature itself and not the value of the growth rate that regulates these activities. In contrast, a foreign periplasmic phosphatase, expressed under the control of its own promoter, displays a different sensitivity toward temperature. We conclude that in the psychrotrophic strain P. fluorescens MF0, growth temperature exerts a specific control upon the activity of certain enzymes. The critical temperature (17.5 degrees C) is within the range of normal growth, suggesting that this control is probably different from a cold shock or heat shock response.
121 citations
TL;DR: The concept on double-(carbon/nitrogen)-limited growth presented here can be extended to other binary and multiple combinations of nutrients.
Abstract: Simultaneous limitation of microbial growth by two or more nutrients is discussed for dual carbon/nitrogen-limited growth in continuous culture. The boundaries of the zone where double-limited growth occurs can be clearly defined from both cultivation data and cellular composition and they can be also predicted from growth yield data measured under single-substrate-limited conditions. It is demonstrated that for the two nutrients carbon and nitrogen the zone of double nutrient limitation is dependent on both the C:N ratio of the growth medium and the growth (dilution) rate. The concept on double-(carbon/nitrogen)-limited growth presented here can be extended to other binary and multiple combinations of nutrients.
111 citations
TL;DR: In N‐limited continuous chemostat cultures of the green alga Haematococcus lacustris (Gir.) Rostaf.
Abstract: In N-limited continuous chemostat cultures of the green alga Haematococcus lacustris (Gir) Rostaf (UTEX 16), the steady-state astaxanthin content of the cells was determined by the specific growth rate of the cultures The highest, pigment content was obtained at the lowest dilution rate The specific rate of astaxanthin accumulation was, however, a function of the photon flux density measured at the illuminated culture surface In nongrowing Haematococcus cultures, the specific rate of astaxanthin accumulation was determined by the growth rate of the culture during growth phase The highest possible cellular astaxanthin content of all cultures was comparable and independent of the culture parameters
93 citations
TL;DR: Ribulose 1,5-bisphosphate carboxylase activities in cell extracts indicated that T. ferrooxidans employs the Calvin cycle for carbon assimilation during growth on formate, and Oxidation of formate by cell extracts was NAD(P) independent.
Abstract: A variety of acidophilic microorganisms were shown to be capable of oxidizing formate. These included Thiobacillus ferrooxidans ATCC 21834, which, however, could not grow on formate in normal batch cultures. However, the organism could be grown on formate when the substrate supply was growth limiting, e.g., in formate-limited chemostat cultures. The cell densities achieved by the use of the latter cultivation method were higher than cell densities reported for growth of T. ferrooxidans on ferrous iron or reduced sulfur compounds. Inhibition of formate oxidation by cell suspensions, but not cell extracts, of formate-grown T. ferrooxidans occurred at formate concentrations above 100 μM. This observation explains the inability of the organism to grow on formate in batch cultures. Cells grown in formate-limited chemostat cultures retained the ability to oxidize ferrous iron at high rates. Ribulose 1,5-bisphosphate carboxylase activities in cell extracts indicated that T. ferrooxidans employs the Calvin cycle for carbon assimilation during growth on formate. Oxidation of formate by cell extracts was NAD(P) independent.
84 citations
TL;DR: In this study special attention is directed to amino acid utilization of mouse hybridoma in batch, chemostat and perfusion fermentations, which shows the considerable difference of amino acid consumption rates in different fermentation modes.
Abstract: Serum free fermentation procedures of cell cultures have got a wide application in production of biochemicals. But, cells cultured in serum free media in general are more sensitive to changes in culture condition, especially to nutrient limitation. There are no substances from serum which can support the cells when conditions are changing. In this study special attention is directed to amino acid utilization of mouse hybridoma in batch, chemostat and perfusion fermentations. Detailed data are presented which show the considerable difference of amino acid consumption rates in different fermentation modes. Already, in batch mode there are differences of the two investigated mouse hybridoma cell lines, although they are derived from the same myeloma line. In chemostat running at a dilution rate representing maximal growth rate most of the consumption rates are significant higher than in batch. On the other hand, in perfusion mode the rates are lower than in batch. This indicates clearly the different conditions of the fermentation modes. Therefore, it is necessary to develop serum free processes under the desired production conditions. An accurate analysis of the process is strongly recommended.
72 citations
TL;DR: The cellular morphology of these cells was studied as a function of time by freeze-fracture electron microscopy, which provided information on changes in membrane ultrastructure and revealed large and small PHA granules in slowly and rapidly growing cells, respectively.
67 citations
TL;DR: The effects of growth rate on production of the antibiotic granaticin, extracellular protein and protease activity as components of secondary metabolism were studied and revealed complex changes in amount which were dependent on growth rate and temperature.
Abstract: Summary: Streptomyces thermoviolaceus was grown in a chemostat under conditions of glutamate limitation. The effects of growth rate on production of the antibiotic granaticin, extracellular protein and protease activity as components of secondary metabolism were studied at 37, 45 and 50 °C. The amount of each secondary metabolite synthesized was highly dependent on growth rate and temperature. Granaticin yields were highest at growth rates of 0·1 to 0·15 h-1 at 37 °C, 0·175 h-1 at 45 °C and 0·045 h-1 at 50 °C. Protease activity of culture supernatants responded to low nutrient concentration and/or low growth rate. Measurements of extracellular protein revealed complex changes in amount which were dependent on growth rate and temperature. At 45 °C and a growth rate of 0·15 h-1, biomass yield was highest between pH 5·5 to 6·5 whereas granaticin synthesis was low at pH 5·5 and rose to highest values at between pH 6·5 and 7·5.
61 citations
TL;DR: It is demonstrated that strictly alkaliphilic B. firmus RAB and two strains of B. alcalophilus (ATCC and DSM 485) grow exponentially in batch cultures with a doubling time of less than 1 h in 100 mM buffered medium, while the actual medium pH remains above 10.2.
Abstract: Alkaliphilic Bacillus species that grow at pH 10.5 must cope with a low protonmotive force (- 50 mV) due to a reversed transmembrane pH gradient at least 2 pH units more acid inside. Here we demonstrate that strictly alkaliphilic B. firmus RAB and two strains of B. alcalophilus (ATCC 27467 and DSM 485) grow exponentially in batch cultures with a doubling time of less than 1 h in 100 mm buffered medium, while the actual medium pH remains above 10.2. The ATCC strain continued to grow rapidly for at least 7 h, but the growth rate of the DSM strain declined dramatically after 3 h. However, both the B. alcalophilus strains, B.firmus RAB and facultatively alkaliphilic B.firmus OF4 were readily maintained for at least 24 h between pH 10.4 and 10.6 in a chemostat where nutrients were constantly replenished. A critical nutrient may be limiting in batch cultures of the DSM strain of B. alcalophilus. The facultative alkaliphile grew equally well in batch cultures at an initial pH of 7.5 or 10.5. Its molar growth yield (23 mg dry wt mmol-1) on malate (Y
mal) was the same at the two pH values and was comparable to Y
mal for B. subtilis grown at neutral pH. B.firmus RAB and B. alcalophilus ATCC 27467 grown at pH 10.5 also showed Y
mal values at least as high as the neutralphile, indicating efficient use of the energy source even at low protonmotive force. Moreover, the phosphorylation potential of B.firmus OF4 grown at pH 7.5 (45.2 kJ mol-1)or pH 10.5 (46 kJ mol-1) was in a conventional range for bacteria.
56 citations
TL;DR: A two‐compartment model for the lactic acid fermentation with Streptococcus cremoris is experimentally verified and both qualitatively and quantitatively the major features of the model are confirmed: the external substrates enter into intracellular high‐energy building blocks, and lactic Acid is formed as a by‐product of these reactions.
Abstract: A two-compartment model for the lactic acid fermentation with Streptococcus cremoris is experimentally verified. The seven parameters of the model are determined using steady-state chemostat data at varying values of dilution rate, D, but with a constant feed concentration, s(f), of a single carbohydrate source (glucose, lactose, or galactose), and a constant feed concentration of s(Nf) of the N source. Steady-state measurements of the RNA content at different exit concentrations, s, of the carbohydrate are included to calculate kinetic parameters that determine the cell composition for varying operating conditions. The model is tested using data from a large set of steady-state and non-steady-state experiments: batch fermentations and step and pulse experiments in a chemostat. Both qualitatively and quantitatively the major features of the model are confirmed: the external substrates enter into intracellular high-energy building blocks, and lactic acid is formed as a by-product of these reactions. Cell growth depends on the fraction of active components (X(A)) of the cell and is not accompanied by lactic acid production. Possible model modifications are discussed, primarily to obtain a better description of lactic acid fermentation at nongrowth conditions.
54 citations
TL;DR: Ammonium ions are transported via the K dp leading to a futile cycle of ammonium ions and ammonia molecules (plus protons) across the cytoplasmic membrane, which would increase the energy requirement of the cells and therefore increase their specific rate of oxygen consumption.
Abstract: Escherichia coli Frag1 was grown under various nutrient limitations in chemostat culture at a fixed temperature, dilution rate and pH both in the presence and the absence of a high concentration of ammonium ions by using either ammonium chloride or dl-alanine as the sole nitrogen source. The presence of high concentrations of ammonium ions in the extracellular fluids of potassium-limited cultures of E. coli Frag1 caused an increase of the specific rate of oxygen consumption of these cultures. In contrast, under phosphate-, sulphate- or magnesium-limited growth conditions no such increase could be observed. The presence of high concentrations of ammonium ions in potassium-limited cultures of E. coli Frag5, a mutant strain of E. coli Frag1 which lacks the high affinity potassium uptake system (Kdp), did not increase the specific rate of oxygen consumption.
TL;DR: Enterococcus faecalis was grown under anaerobic conditions in chemostat cultures on energy sources with different degress of reduction and intracellular NADH/NAD ratios were measured and were found to be influenced both by the nature of the energy source and by the culture pH value.
Abstract: Enterococcus faecalis was grown under anaerobic conditions in chemostat cultures on energy sources with different degress of reduction (i.e. mannitol, glucose, pyruvate) at various culture pH values. Intracellular NADH/NAD ratios were measured and were found to be influenced both by the nature of the energy source and by the culture pH value. Highest ratios were found with mannitol as energy source and with high culture pH values. A role for the redox potential of the NADH/NAD couple as a regulatory effector is suggested by a correlation of the redox potential with the in vivo distribution of the carbon flux between pyruvate formate lyase and the pyruvate dehydrogenase complex.
TL;DR: A Generalized Maintenance Energy (GME) model is proposed, to take account of the effects of culture stress on the nutrient uptake rates and agreed very well with other mouse-mouse hybridoma chemostat culture data in the literature.
Abstract: Experimental data collected from bench-scale chemostat cultures of mouse-mouse hybridoma cells have been used for the development of a kinetic model of monoclonal antibody production. The specific antibody productivity was found to be proportional to the specific death rate, indicating a stimulating effect of stress on the ability of the cells to produce antibody. The death rate was found to be an exponential function of the average cell age in the culture. Furthermore, a Generalized Maintenance Energy (GME) model is proposed, to take account of the effects of culture stress on the nutrient uptake rates. The proposed relationships agreed very well with other mouse-mouse hybridoma chemostat culture data in the literature.
TL;DR: The apparatus was used to select organisms with growth and attachment characteristics that could not be evaluated by conventional batch, or chemostat, culture conditions, and model calculations illustrate the utility of this flow pattern in the selection and maintenance of slow-growing, adherent organisms.
Abstract: A bioreactor apparatus is described for studying bacterial attachment. A cyclic, on-off, flow regime was imposed within the apparatus. Model calculations illustrate the utility of this flow pattern in the selection and maintenance of slow-growing, adherent organisms. The apparatus is believed to have general utility in testing bacterial attachment influenced by many types of experimental or environmental constraints, including variations in fluid dynamics, presence of toxic substances (metals or organics), nature of the substratum surface, concentrations of limiting nutrients, and competition between bacterial strains. As an example application, the apparatus was employed to test 14 bacterial strains for surface attachment in a nutrient-limited growth medium. The medium was developed, using the chemical equilibrium program MINEQL, for planned studies of biofilms in a solution with a chemically defined composition that permits calculation of trace metal speciation. The apparatus was used to select organisms with growth and attachment characteristics that could not be evaluated by conventional batch, or chemostat, culture conditions. When supplied with acetate, pyruvate, or succinate as a carbon and energy source, the gram-negative strains Pseudomonas cepacia 17616 and Zoogloea sp. WGO4 showed superior attachment characteristics to glass surfaces in the chemically defined medium but only moderate fluid-phase growth. The gram-positive Arthrobacter sp. strain 9G4D and gram-negative species P. pickettii and Zoogloea sp. WNJ8, when supplied with pyruvate as a carbon and energy source, were capable of superior growth in the fluid phase but formed only a low to moderate biofilm surface coverage.
TL;DR: A system of ordinary differential equations is used to model the interactions of n competing predators on a single prey population in a chemostat environment with a periodic nutrient input.
Abstract: A system of ordinary differential equations is used to model the interactions of n competing predators on a single prey population in a chemostat environment with a periodic nutrient input. In the case of one or no predators, criteria for the existence of periodic solutions are given. In the general case, conditions for all populations to persist are derived.
TL;DR: In synchronized continuous cultures of Saccharomyces cerevisiae CBS 8066, the production of the extracellular invertase showed a cyclic behavior that coincided with the budding cycle, which resulted in cyclic changes in amounts of inverts localized in the cell wall.
Abstract: In synchronized continuous cultures of Saccharomyces cerevisiae CBS 8066, the production of the extracellular invertase (EC 3.2.1.26) showed a cyclic behavior that coincided with the budding cycle. The invertase activity increased during bud development and ceased at bud maturation and cell scission. The cyclic changes in invertase production resulted in cyclic changes in amounts of invertase localized in the cell wall. However, the amount of enzyme invertase present in the culture liquid remained constant throughout the budding cycle. Also, in asynchronous continuous cultures of S. cerevisiae, the production and localization of invertase showed significant fluctuation. The overall invertase production in an asynchronous culture was two to three times higher than in synchronous cultures. This could be due to more-severe invertase-repressive conditions in a synchronous chemostat culture. Both the intracellular glucose-6-phosphate concentration and residual glucose concentration were significantly higher in synchronous chemostat cultures than in asynchronous chemostat cultures. In the asynchronous and synchronous continuous cultures of S. cerevisiae, about 40% of the invertase was released into the culture liquid; it has generally been believed that S. cerevisiae releases only about 5% of its invertase. In contrast to invertase production and localization in the chemostat cultures of S. cerevisiae, no significant changes in inulinase (EC 3.2.1.7) production and localization were observed in chemostat cultures of Kluyveromyces maxianus CBS 6556. In cultures of K. marxianus about 50% of the inulinase was present in the culture liquid.
TL;DR: Growth of the acetogenic anaerobe Eubacterium limosum on methanol/CO2 mixtures is limited by the rate at which CO2 can be assimilated, but this limitation can be offset by the consumption of acetate as an additional co-substrate.
Abstract: Summary: Growth of the acetogenic anaerobe Eubacterium limosum on methanol/CO2 mixtures is limited by the rate at which CO2 can be assimilated. This limitation can be offset by the consumption of acetate as an additional co-substrate. Growth on methanol/CO2/acetate mixtures improves growth rates but stimulates production of an unidentified polymer leading to cell aggregation and wall growth under chemostat conditions. Production of butyrate as major fermentation end-product leads to growth inhibition visualized by an increased maintenance requirement as demonstrated by Y
ATP estimations.
TL;DR: It has been concluded that for a good analysis of the growth behaviour of filamentour fungi the linear equation for substrate utilization is not suitable, since it contains no term for the process of differentiation.
Abstract: Aspergillus niger has been grown in glucose- and maltose-limited continuous cultures to determine the bioenergetic consequences of the production of the extracellular enzyme glucoamylase. Growth yields (g biomass per mol substrate) were high, indicating that growth was very efficient and protein production for biomass was not exceedingly energy consuming. It has been found that the energy costs for the production of this extracellular enzyme is very high. Depending on the efficiency of energy conservation the glucoamylase protein yield on ATP is between 1.3 and 2.6 g protein per mol ATP, which is equal or less than 10% of the theoretical maximum of 25.5. These high energy costs most probably have to be invested in the process of excretion. A comparison between an industrial over-producing strain and the wild typeAspergillus niger showed that this over-producing strain most probably is a regulatory mutant. Two regions of specific growth rates could be determined (one at specific growth rates lower and one at specific growth rates higher than 0.1 h-1), which are characterized by differences in mycelium morphology and a significant deviation from linearity in the linear equation for substrate utilization. Analysis of the region of specific growth rates higher than 0.1 h-1 yielded maintenance requirements of virtual zero. It has been concluded that for a good analysis of the growth behaviour of filamentour fungi the linear equation for substrate utilization is not suitable, since it contains no term for the process of differentiation.
TL;DR: For a relaxed (rel-), protease producing (A-type) and a stringent (rel+), not-protease-producing (B-) variant of Bacillus licheniformis, this paper determined fermentation patterns and products, growth parameters and alkaline protease production (if any) in anaerobic, glucose-grown chemostats and batch-cultures.
Abstract: For a relaxed (rel-), protease producing (A-type) and a stringent (rel+), not-protease producing (B-type) variant of Bacillus licheniformis we determined fermentation patterns and products, growth parameters and alkaline protease-production (if any) in anaerobic, glucose-grown chemostats and batch-cultures. Glucose is dissimilated via glycolysis and oxidative pentose phosphate pathway simultaneously; the relative share of these two routes depends on growth phase (in batch) and specific growth rate (in chemostat). Predominant products are lactate, glycerol and acetaldehyde for A-type batches and acetaldehyde, ethanol, acetate and lactate for B-type batches. Both types show a considerable acetaldehyde production. In chemostat cultures, the fermentation products resemble those in batch-culture.
TL;DR: Comparison of batch mode, chemostat operation and pHstat-turbidostatic control showed that productivities for the continuous process were greater than that for the batch operation, and an expanded Luedeking-Piret model of product formation kinetics fits the observed che mostat data and demonstrates that the production of pertussis toxin is predominantly growth associated.
TL;DR: The influence of the growth rate on the accumulation of ergosterol inSaccharomyces cerevisiae was studied with glucose and ethanol as substrates under P-limitation in chemostat experiments and results indicated that above this dilution rate an increase in ergosterols content occurred.
Abstract: The influence of the growth rate on the accumulation of ergosterol inSaccharomyces cerevisiae was studied with glucose and ethanol as substrates under P-limitation in chemostat experiments. In cultures with glucose as carbon source a decrease in ergosterol content with dilution rates up to 0.08 h−1 was observed, whereas above this dilution rate an increase in ergosterol content occurred. Similar but less marked effects were attained with ethanol as carbon source. A maximum specific rate of ergosterol synthesis of about 2.4 mg per h and g dry cell mass was calculated for phosphorus limited cultures.
TL;DR: It is suggested that the cause of this inhibition resides in depletion of the NADPH pool due to the high rate at which NADPH is oxidized by 2-ketogluconate reductase.
Abstract: Summary: Klebsilla pneumoniae NCTC 418 is able to convert 2-ketogluconate intracellularly to 6-phosphogluconate by the combined action of an NADPH-dependent 2-ketogluconate reductase and gluconate kinase. Synthesis of the former enzyme was maximal under 2-ketogluconate-Iimited growth conditions. An instantaneous transition to a 2-ketogluconate-excess condition resulted in an acceleration of catabolism of this carbon source, accompanied by complete inhibition of biosynthesis. It is suggested that the cause of this inhibition resides in depletion of the NADPH pool due to the high rate at which NADPH is oxidized by 2-ketogluconate reductase.
TL;DR: The data suggest that the biofilm cells of P. aeruginosa switch on the expression of IROMPs to assist iron acquisition when the dilution rate used for the chemostat run is below 0.5 h-1.
Abstract: An in vitro chemostat system was used to study the growth and the expression of iron-regulated outer-membrane proteins (IROMPs) by biofilm cells of Pseudomonas aeruginosa cultivated under condition
TL;DR: In methanol-limited chemostat culture a pH optimum at 7.0 with a narrow growth rate optimum with respect to growth yield and metabolic uncoupling was revealed and the organism displayed a low maintenance energy and high maximum specific growth rate.
Abstract: The regulation of carbon metabolism in a pink-pigmented facultative methylotroph has been studied. In methanol-limited chemostat culture a pH optimum at 7.0 with a narrow growth rate optimum with respect to growth yield and metabolic uncoupling was revealed. The average growth yield was 14±0.036 g·mol−1 and the organism displayed a low maintenance energy and high maximum specific growth rate. When the carbon concentration in the feed remained constant and the dilution rate increased a deviation from linearity between substrate consumption and growth rate was found at higher growth rates. The addition of a pulse of methanol to a carbon-limited culture showed that anabolism could be dissociated from catabolism with the resulting accumulation of formaldehyde in concentrations which were not lethal.
TL;DR: With variously limited chemostat cultures of Bacillus stearothermophilus, the glucose consumption rate increased markedly as the concentration of dissolved oxygen was lowered from 50% to 1% air saturation and the specific rate of acetate production increased and lactate accumulated in large amounts.
Abstract: Summary: With variously limited chemostat cultures of Bacillus stearothermophilus, the glucose consumption rate increased markedly as the concentration of dissolved oxygen (d.o.t.; dissolved oxygen tension) was lowered from 50% to 1% air saturation. Concomitantly, the specific rate of acetate production increased and lactate, which was not present in the fully aerobic cultures, accumulated in large amounts. Moreover, whereas at a high d.o.t. only an ammonia-limited culture excreted 2-oxoglutarate, all glucose-sufficient cultures excreted this metabolite at a d.o.t. of 1% air saturation, even more being produced by a K+-limited culture than by the ammonia-limited one. The activities of those enzymes of glycolysis that were measured increased in parallel with the glucose consumption rate, as did the activities of enzymes of the Entner-Douderoff pathway. Similarly, the activities of lactate dehydrogenase and acetate kinase (which were synthesized constitutively also) reflected the corresponding metabolite production rates. Tricarboxylic acid (TCA) cycle activity markedly diminished with a lowering of the available oxygen supply and again (with the exception of aconitase and 2-oxoglutarate dehydrogenase) this was mirrored in decreases in the activities of TCA cycle enzymes. Assessments of energy flux in terms of ATP equivalents suggested that it was energetically more expensive to synthesize biomass at a low d.o.t. than at a high one. However, the presence of enzymes of the methylglyoxal bypass (methylglyoxal synthase and glyoxylase) at high activities in cells grown at a low d.o.t. render assessments of ATP flux rates unreliable.
TL;DR: Escherichia coli strains J53(nal) and J53 (RP4) were grown together in glucose-limited continuous cultures and the difference between the predicted growth-rate potentials of the two strains was increased by selection of a chemostat-adapted variant of J 53(RP4).
Abstract: Escherichia coli strains J53(nal) and J53(RP4) were grown together in glucose-limited continuous cultures. Based on the measured growth kinetic constants of the two strains, take-over of the cultur...
Journal Article•
TL;DR: Steady state growth of the red alga Porphyridium cruentum was obtained in light-limited chemostat cultures at different temperatures, pH and salinities over a range of specific growth rates and the maintenance energy was found to be virtually zero under all conditions.
Abstract: summary
Steady state growth of the red alga Porphyridium cruentum was obtained in light-limited chemostat cultures at different temperatures, pH and salinities over a range of specific growth rates. Geometric design of the reactors was found to have no effect on the yield and photosynthetic efficiency (PE) of the biomass. Under optimal growth conditions, that is at 23 °C, pH 8 and NaCl concentration of 0.42 M, the maximum specific growth rate was 0.065h−l which corresponded to a generation time of 10.7 h. With a given light input the biomass output rate was found to be constant over the range of specific growth rates studied. The values of the maximum growth yield (YG) and maximum PE of P. Cruentum were in the range of 0.0064–0.0074 g kj−1 and 13.4–15.5% respectively, when growth was optimal. This PE value corresponds to a quantum demand of 15 per O2 molecule evolved. Different temperatures, pH and salinities were demonstrated to cause a 1.5 to 2-fold variation in the maximum PE. The maintenance energy was found to be virtually zero under all conditions.