Showing papers on "Chemostat published in 1995"
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01 Jan 1995TL;DR: The simple chemostat with an inhibitor and the general gradostat with a periodic washout rate have been used in nonlinear nonlinear analysis as mentioned in this paper, and convergence theorem has been proved.
Abstract: 1. The simple chemostat 2. The general chemostat 3. Competition on three trophic levels 4. The chemostat with an inhibitor 5. The simple gradostat 6. The general gradostat 7. The chemostat with periodic washout rate 8. Variable yield models 9. A size-structured competition model 10. New directions 11. Open questions Appendix A. Matrices and their eigenvalues Appendix B. Differential inequalities Appendix C. Monotone systems Appendix D. Persistence Appendix E. Some techniques in nonlinear analysis Appendix F. A convergence theorem.
627 citations
TL;DR: It is concluded that, during carbon‐limited growth of S. cerevisiae on mixtures of glucose and ethanol, biosynthetic intermediates with three or more carbon atoms are preferentially synthesized from glucose.
Abstract: Growth efficiency and regulation of key enzyme activities were studied in carbon- and energy-limited chemostat cultures of Saccharomyces cerevisiae grown on mixtures of glucose and ethanol at a fixed dilution rate. Biomass yields on substrate carbon and oxygen could be adequately described as the net result of growth on the single substrates. Activities of isocitrate lyase and malate synthase were not detected in cell-free extracts of glucose-limited cultures. However, both enzymes were present when the ethanol fraction in the reservoir medium exceeded the theoretical minimum above which the glyoxylate cycle is required for anabolic reactions. Fructose-1,6-bisphosphatase activity was only detectable at high ethanol fractions in the feed, when activity of this enzyme was required for synthesis of hexose phosphates. Phospho-enol-pyruvate-carboxykinase activity was not detectable in extracts from glucose-grown cultures and increased with the ethanol fraction in the feed. It is concluded that, during carbon-limited growth of S. cerevisiae on mixtures of glucose and ethanol, biosynthetic intermediates with three or more carbon atoms are preferentially synthesized from glucose. Synthesis of the key enzymes of gluconeogenesis and the glyoxylate cycle is adapted to the cells' requirement for these intermediates. The gluconeogenic enzymes and their physiological antagonists (pyruvate kinase, pyruvate carboxylase and phosphofructokinase) were expressed simultaneously at high ethanol fractions in the feed. If futile cycling is prevented under these conditions, this is not primarily achieved by tight control of enzyme synthesis.
157 citations
TL;DR: The results indicated an increase in the relative energy needed for maintenance to overcome sulfide inhibition and uncoupling growth from energy production, however, D. desulfuricans to some extent could recover from the shock of high sulfide concentrations and was suggested to incorporate the sulfide product inhibition kinetics in a variety of applications.
122 citations
TL;DR: The major finding is that the correlation between substrate availability and cellular growth rate found for the free-living cells was not observed for the surface-bound cells, and the data indicate an almost constant growth rate for attached cells which was independent of the dilution rate in the chemostat.
Abstract: A fast routine method for estimating bacterial cell growth rates by using the metachromatic dye acridine orange is described. The method allows simultaneous estimates of cellular RNA and DNA contents of single cells. Acridine orange staining can be used as a nonspecific supplement to quantitative species-specific hybridizations with fluorescence-labelled ribosomal probes to estimate the single-cell concentration of RNA. By automated analysis of digitized images of stained cells, we determined four independent growth rate-related parameters: cellular RNA and DNA contents, cell volume, and the frequency of dividing cells in a cell population. These parameters were used to compare physiological states of liquid-suspended and surface-growing Pseudomonas putida KT2442 in chemostat cultures. The major finding is that the correlation between substrate availability and cellular growth rate found for the free-living cells was not observed for the surface-bound cells; in contrast, the data indicate an almost constant growth rate for attached cells which was independent of the dilution rate in the chemostat.
116 citations
TL;DR: The two-stage chemostat appeared to be very effective for hydrogen production, allowing complete nitrogen removal by bacterial growth in the first reactor, and opposite trends of decreasing bacterial activity and increasing concentration resulted in a linear increase of the overall hydrogen production.
Abstract: Rhodobacter sphaeroides RV cultivation and hydrogen production were studied in a one- and two-stage chemostat using lactic acid as substrate. Light saturation was observed when light intensities equal to or above 10 klx were applied. Under light saturation, the two-stage chemostat appeared to be very effective for hydrogen production, allowing complete nitrogen removal by bacterial growth in the first reactor. The hydrogen evolution rate in the second reactor was up to 75 ml H2 (g dry weight)−1 h−1. Accumulation of storage material was observed in the second reactor of the two-stage chemostat under a large carbon excess and limiting light irradiance. The optimal hydraulic residence time was 15 h for both stages, leading to a total hydrogen production about 40% higher than in the one-stage chemostat. Under increasing influent ammonium and yeast extract concentrations, opposite trends of decreasing bacterial activity and increasing concentration resulted in a linear increase of the overall hydrogen production to 1.4–1.6lH2 (l reactor)−1 day−1. Hydrogen production quickly fell when nitrogen was not completely metabolised. The hydrogen evolution rate was also found to depend on lactic acid concentration, and maximum bacterial activity was observed at 100 mM influent lactic acid.
108 citations
TL;DR: In this article, the effects of growth conditions on mitochondrial morphology were studied in living Saccharomyces cerevisiae cells by vital staining with the fluorescent dye dimethyl-aminostyryl-methylpyridinium iodine (DASPMI), fluorescence microscopy, and confocal-scanning laser microscopy.
Abstract: Effects of growth conditions on mitochondrial morphology were studied in living Saccharomyces cerevisiae cells by vital staining with the fluorescent dye dimethyl-aminostyryl-methylpyridinium iodine (DASPMI), fluorescence microscopy, and confocal-scanning laser microscopy. Cells from respiratory, ethanol-grown batch cultures contained a large number of small mitochondria. Conversely, cells from glucose-grown batch cultures, in which metabolism was respiro-fermentative, contained small numbers of large, branched mitochondria. These changes did not significantly affect the fraction of the cellular volume occupied by the mitochondria. Similar differences in mitochondrial morphology were observed in glucose-limited chemostat cultures. In aerobic chemostat cultures, glucose metabolism was strictly respiratory and cells contained a large number of small mitochondria. Anaerobic, fermentative chemostat cultivation resulted in the large, branched mitochondrial structures also seen in glucose-grown batch cultures. Upon aeration of a previously anaerobic chemostat culture, the maximum respiratory capacity increased from 10 to 70 mumole.min-1.g dry weight-1 within 10 h. This transition resulted in drastic changes of mitochondrial number, morphology and, consequently, mitochondrial surface area. These changes continued for several hours after the respiratory capacity had reached its maximum. Cyanide-insensitive oxygen consumption contributed ca. 50% of the total respiratory capacity in anaerobic cultures, but was virtually absent in aerobic cultures. The response of aerobic cultures to oxygen deprivation was qualitatively the reverse of the response of anaerobic cultures to aeration. The results indicate that mitochondrial morphology in S. cerevisiae is closely linked to the metabolic activity of this yeast: conditions that result in repression of respiratory enzymes generally lead to the mitochondrial morphology observed in anaerobically grown, fermenting cells.
89 citations
TL;DR: The continuous cultivation with smooth and constant increase of dilution rate (A-stat) proved itself as a powerful experimental method for the study of the behaviour of growth characteristics.
76 citations
TL;DR: Experimental evidence that in vivo catabolite repression by glucose is absent at the very low glucose concentrations present in che mostat culture is given and chemostat-grown cells of E. coli are able to substitute glucose as a carbon and energy source by several other sugars with no lag period.
Abstract: SUMMARY: It was investigated whether Escherichia coli cultured in a glucose-limited chemostat is able to grow with a series of sugars whose utilization is normally repressed during batch growth with glucose. Cells growing at dilution rates of 0·2, 0·3 and 0·6 h-1 were able to immediately utilize and grow with fructose mannose, maltose and ribose. Galactose was transported instantaneously but growth started only after a considerable lag. Arabinose was the only sugar tested which was neither transported nor utilized immediately. The results give experimental evidence that in vivo catabolite repression by glucose is absent at the very low glucose concentrations present in chemostat culture. Additionally, the results demonstrate that chemostat-grown cells of E. coli are able to substitute glucose as a carbon and energy source by several other sugars with no lag period.
71 citations
TL;DR: The coexistence state obtained in the periodically operated chemostat is usually periodic, but cases of quasi-periodic and chaotic behavior are also observed.
Abstract: Coexistence of three microbial populations engaged in pure and simple competition is not possible in a chemostat with time-invariant operating conditions under any circumstances. It is shown that by periodic variation of the chemostat dilution rate it is possible to obtain a stable coexistence state of all three populations in the chemostat. This is accomplished by performing a numerical bifurcation analysis of a mathematical model of the system and by determining its dynamic behavior with respect to its operating parameters. The coexistence state obtained in the periodically operated chemostat is usually periodic, but cases of quasi-periodic and chaotic behavior are also observed.
64 citations
TL;DR: Transient data indicate that the maximum rate of glucose consumption at a particular set of operating conditions is correlated to the metabolic 'capacity' of the mold as reflected by its intracellular RNA content.
61 citations
TL;DR: The effects of produced ethanol and specific growth rate on the lipid content and composition of Saccharomyces cerevisiae CBS 2806 were studied using anaerobic chemostat cultures.
Abstract: The effects of produced ethanol and specific growth rate on the lipid content and composition of Saccharomyces cerevisiae CBS 2806 were studied using anaerobic chemostat cultures The cells adapted to increased concentrations of produced ethanol by increasing the proportion of ergosterol at the expense of lanosterol, by increasing the proportion of phosphatidylinositol at the expense of phosphatidylcholine, and by increasing the amount of C18:0 fatty acids in total phospholipids at the expense of C16:0 fatty acids The produced ethanol had no effect on the phospholipid content nor on the proportion of unsaturated fatty acids in the phospholipids The specific growth rate had no effect on the phospholipid content, the sterol composition, the phospholipid composition, the fatty acid composition of total phospholipids, or on the proportion of unsaturated fatty acids in the phospholipids of S cerevisiae It was not possible to separate the effects of produced ethanol and growth rate on the ergosterol content of the chemostat-grown S cerevisiae cells
TL;DR: Strong starvation promoters have recently been clones and characterized in environmentally relevant bacteria like Pseudomonas species; thus, starvation promoter-driven degradative systems can be constructed in such bacteria and tested for in situ efficacy.
Abstract: The expression of much useful bacterial activity is facilitated by rapid growth. This coupling can create problems in bacterial fermentations and in situ bioremediation. In the latter process, for example, it necessitates addition of large amounts of nutrients to contaminated environments, such as aquifers. This approach, termed biostimulation, can be technically difficult. Moreover, the resulting in situ bacterial biomass production can have undesirable consequences. In an attempt to minimize coupling between expression of biodegradative activity and growth, we used Escherichia coli starvation promoters to control toluene monooxygenase synthesis. This enzyme complex can degrade the environmental contaminants trichloroethylene (TCE) and phenol. Totally starving cell suspensions of such strains degraded phenol and TCE. Furthermore, rapid conversions occurred in the postexponential batch or very slow growth (dilution) rate chemostat cultures, and the nutrient demand and biomass formation for transforming a given amount of TCE or phenol were reduced by 60 to 90%. Strong starvation promoters have recently been clones and characterized in environmentally relevant bacteria like Pseudomonas species; thus, starvation promoter-driven degradative systems can now be constructed in such bacteria and tested for in situ efficacy.
TL;DR: A model of competition in the chemostat with an inhibitor is combined with a model of Competition in theChemostat between plasmid-bearing and plasmids-free organism to produce a model that more closely approximates the way che mostat-like devices are used in biotechnology.
Abstract: A model of competition in the chemostat with an inhibitor is combined with a model of competition in the chemostat between plasmid-bearing and plasmid-free organism to produce a model that more closely approximates the way chemostat-like devices are used in biotechnology. The asymptotic behavior of the solutions of the resulting system of nonlinear differential equations is analyzed as a function of the relevant parameters. The techniques are those of dynamical systems although perturbation techniques are used when the parameter reflecting plasmid-loss is small.
TL;DR: A method for the accurate quantitative determination of net proton production or consumption in biological cultures has been devised and this equivalence is independent of the buffering capacity of the culture medium.
Abstract: In this investigation, a method for the accurate quantitative determination of net proton production or consumption in biological cultures has been devised. Cells are cultured under constant pH conditions. The specific rate of proton production or consumption by the culture (qH+, mmol h-1 per g biomass) is proportional to the mmol of base or acid required to maintain constant pH per unit time, and this equivalence is independent of the buffering capacity of the culture medium. The above method has been applied to chemostat cultures of Candida utilis growing on glucose or glycerol as carbon source, and different nitrogen sources. The results indicate that the nitrogen assimilation pathway alone determines the value of qH+, and a fixed stoichiometric relationship between nitrogen uptake rate qN (meq h-1 per g biomass) and qH+ has been found for each nitrogen source employed. Thus, qH+/qN values of +1, 0 and -1 were found for ammonium ions, urea and nitrate respectively. Under oxidative metabolism, the contribution of carbon catabolism to the value of qH+ was undetectable. Sine qN may be related to growth and production of type 1 compounds in fermentation processes, the parameter qH+ was incorporated into a model of growth and energy metabolism in chemostat culture (Castrillo and Ugalde, Yeast 10, 185 - 197, 1994), resulting in adequate simulations of experimentally observed culture performance. Thus, it is suggested that qH+ may be employed as a simple and effective control parameter for biotechnological processes involving biomass-related products.
TL;DR: Cell metabolism in the reactor was found to vary with the extent of cell retention, which determined both cell density and specific growth rate, which can be used to culture cell lines with widely different productivity patterns.
Abstract: Suspended mammalian cells can be cultivated in a variety of operational modes (pure chemostat, total cell retention, or partial cell retention) in a homogeneous perfusion bioreactor by varying the cell bleed rate. Hybridomas were grown in the reactor at a perfusion rate of 2.0 day -1 for over 10 weeks at different specific growth rates and viable cell densities achieved by varying the extent of cell retention. Cell metabolism in the reactor was found to vary with the extent of cell retention, which determined both cell density and specific growth rate. With partial cell retention, the nutrient consumption and metabolite production rates decreased with both increasing growth rate and increasing cell density. The specific and volumetric antibody production rates, however, increased dramatically with cell density (and to a lesser extent with decreasing growth rate). The specific MAb production rate was lower with total cell retention than with partial retention at the same growth rate. Since the reactor can be operated over a range of perfusion rates and extents of cell retention, the system can be used to culture cell lines with widely different productivity patterns.
TL;DR: In this article, the mathematical properties of chemostat equations with delayed growth and delayed nutrient recycling are summarized and the authors show that the properties of these equations are similar to those of the Chemostat equation with delay.
Abstract: The mathematical properties of chemostat equations with delayed growth and delayed nutrient recycling are summarized.
TL;DR: A bioreactor system for the continuous cultivation of animal cells with a high potential for scale-up and the reproducibility of the cell activity under certain process conditions could be demonstrated in fermentations up to 77 days is presented.
Abstract: A bioreactor system for the continuous cultivation of animal cells with a high potential for scale-up is presented. This reactor system consists of radial-flow fixed-bed units coupled with a dialysis module. The dialysis membrane enables the supply of low-molecular-weight nutrients and removal of toxic metabolites, while high-molecular-weight nutrients and products (e.g. monoclonal antibodies) are retained and accumulated. This concept was investigated on the laboratory scale in a bioreactor with an integrated dialysis membrane. The efficiency of the reactor system and the reproducibility of the cell activity (hybridoma cells) under certain process conditions could be demonstrated in fermentations up to 77 days. Based on model calculations, an optimized fermentation strategy was formulated and experimentally confirmed. Compared to chemostat cultures with suspended cells, a ten-times higher mAb concentration (383 mgl−1) could be obtained. The highest volumetric specific mAb production rate determined was 6.1 mg mAb (1 fixed bed)−1 h−1.
TL;DR: Four eubacterial strains able to grow on carbon disulfide (CS2) as sole energy substrate were isolated from soil and leaves of the CS2-producing tree Quercus lobata, extending the range of eubacteria known to be capable of CS2 breakdown and demonstrating that several types of facultatively chemolithotrophic bacteria, ability to grow exclusively on CS2, are associated with a CS2 -producing plant.
Abstract: Four eubacterial strains able to grow on carbon disulfide (CS2) as sole energy substrate were isolated from soil and leaves of the CS2-producing tree Quercus lobata. Three of the isolates (strains KS1, KS2, and KL1) were gram-negative, facultatively methylotrophic, and heterotrophic, and capable of growth on a wide range of inorganic and organic sulfur compounds. Biochemical and physiological properties differed slightly among the three strains, but all are proposed to be novel thiobacillus species. Growth yields on CS2 in batch and chemostat culture ranged from 3.3 g dry wt/mol CS2 (batch) to a maximum growth yield (Ymax) of 11.1 g dry wt/mol (chemostat). Chemostat data for two of the strains growing, autotrophically on thiosulfate gave Ymax values of 7.4 and 7.1 g dry wt/mol, which fall within the range observed with thiobacilli. The three new Thiobacillus strains had DNA containing 39.8 (KS2), 47.8 (KS1), and 50.5 (KL1) mol% G+C. All three were unusual in being able to grow not only on thiosulfate (aerobically or with denitrification), but also on CS2, carbonyl sulfide and methylated sulfides as sole energy substrates, and one was unique in being able to grow also on substituted thiophenes. They are the first organisms described to be capable, of anaerobic growth with denitrification on CS2. The fourth isolate (strain KL2) was gram-positive non-motile and nonspore-forming, with 39.0 mol% G+C. It had a restricted range of sulfur-containing growth substrates, could not grow methylotrophically or on autotrophic substrates other than CS2, and is not yet classifiable These organisms extend the range of eubacteria known to be capable of CS2 breakdown and demonstrate that several types of facultatively chemolithotrophic bacteria, able to grow exclusively on CS2, are associated with a CS2-producing plant.
TL;DR: The discrepancy between the behaviour of shake-flask and chemostat cultures during growth on mineral medium illustrates the necessity of physiological studies for the scalling-up of heterologous protein production from laboratory to production scale.
Abstract: Growth conditions relevant for the large-scale production of heterologous proteins with yeasts were studied on a laboratory scale. A strain of Kluyveromyces lactis, containing 15 copies of an expression cassette encoding guar α-galactosidase integrated into its ribosomal DNA, was used as a model. By using urea as a nitrogen source, it was possible to produce active extracellular α-galactosidase in shake-flask cultures grown on a defined mineral medium. Inclusion of urea instead of ammonium sulphate prevented unwanted acidification of cultures. With urea-containing mineral medium, enzyme production in shake flasks was comparable to that in complex media containing peptone. In contrast, the presence of peptone was required to achieve high productivity in chemostat cultures. The low productivity in chemostat cultures growing on mineral media was not due to loss oft the expression cassette, since addition of peptone to such cultures resulted in an immediate high rate of α-galactosidase production. The discrepancy between the behaviour of shake-flask and chemostat cultures during growth on mineral medium illustrates the necessity of physiological studies for the scalling-up of heterologous protein production from laboratory to production scale.
TL;DR: This paper provides a mathematically rigorous analysis of the global asymptotic behavior of the governing equations in the cases of combinations of inhibited and uninhibited specific growth rates.
Abstract: A model of competition between plasmid-bearing and plasmid-free organisms in a chemostat was proposed in a paper of Stephanopoulis and Lapidus. The model was in the form of a system of nonlinear ordinary differential equations. Such models were relevant to commercial production by genetically altered organisms in continuous culture. The analysis there was local. The rigorous global analysis was done in a paper of Hsu, Waltman and Wolkowicz in the case of the uninhibited specific growth rates. This paper provides a mathematically rigorous analysis of the global asymptotic behavior of the governing equations in the cases of combinations of inhibited and uninhibited specific growth rates.
TL;DR: This technique proved to be successful for studying bacterial adhesion and biofilm formation in tubular devices by bacterial populations at controlled and low growth rates.
Abstract: The combination of a modified Robbins device (MRD) attached to the effluent line of a continuous cultivation vessel was assessed by the adhesion of planktonic bacteria maintained at a controlled growth rate. This combination of a chemostat and an MRD provides a large number of sample surfaces for monitoring both the formation and control of biofilms over extended periods of time. This apparatus was used to monitor the colonization of two soil isolates,Pseudomonas fluorescens (EX101) andPseudomonas putida (EX102) onto silastic rubber surfaces. At a similar μrel, both bacteria attached to the silastic, howeverP. fluorescens formed confluent, dense biofilms in less than 24 h, whereasP. putida adhered as single cells or microcolonies after the same period. The metabolic activity, measured by INT-formazan formation, was similar for both organisms with a peak at 6 h of colonization and a subsequent decrease after 24 h. Long term colonization studies ofP. fluorescens produced a population of greater than 9.5 log cfu cm−2 at 28 days demonstrating the advantages of the chemostat-MRD association. This technique proved to be successful for studying bacterial adhesion and biofilm formation in tubular devices by bacterial populations at controlled and low growth rates.
TL;DR: Antibiotic production in Saccharopolyspora erythraea was significantly enhanced in cyclic fed batch culture (c.f.b.c.c) compared to batch culture, whereas chemostat culture resulted in reduced production.
Abstract: Antibiotic production in Saccharopolyspora erythraea was significantly enhanced in cyclic fed batch culture (c.f.b.c) compared to batch culture, whereas chemostat culture resulted in reduced production. C.f.b.c. allowed the specific growth rate to be varied, with time, according to an asymptotically decreasing trajectory without the necessity for nutrient exhaustion. It was, therefore, possible to increase productivity by increasing the growth-limiting substrate concentration. It was necessary to apply the c.f.b.c regime to early-exponential-phase cultures in order to obtain a stable, nutrient-limited, c.f.b.c. The antibiotic production rate during any c.f.b.c. cycle was dependent on the relationship between the specific growth rate at the time and the growth rate at the start of the cycle.
TL;DR: The effects of vitamin B12 availability on the physiology of the cyanobacterium Syrzechococ~cus sp.
Abstract: The effects of vitamin B12 availability on the physiology of the cyanobacterium Syrzechococ~cus sp. strain PCC 7002 were examined in a continuous culture chemostat system. The availability of vitamin B12 within the system was demonstrated to control the cell density and cellular chlorophyll levels under nutrient-limiting conditions. Electron micrographs of vitamin B12 replete and vitamin B12 deficient cyanobacteria indicated that a reduction in vitamin B12 availability induced a loss of thylakoid integrity within the system. Polyacrylamide gel electrophoresis demonstrated that the expression of outer membrane proteins of 95,70, and 34 kDa was enhanced during vitamin B12 limited growth. Cellular quotieilts were determined to be a minimum of 256 molecules of vitamin B12/cell to sustain a growth rate of 0.6/day. A comparison with eukaryotic plankton demonstrated that the vitamin B12 requirements of cyanobacteria may be more similar to those of chloroplasts than to those of the entire group of eukaryotic algae.
TL;DR: Screening in batch cultures identified Debaryomyces yamadae as a yeast that exhibits the Kluyver effect for sucrose: this disaccharide can be respired but, even under oxygen-limited conditions, alcoholic fermentation of sucrose does not occur.
Abstract: Screening in batch cultures identified Debaryomyces yamadae as a yeast that exhibits the Kluyver effect for sucrose: this disaccharide can be respired but, even under oxygen-limited conditions, alcoholic fermentation of sucrose does not occur. Ethanol, glycerol and arabitol were the main fermentation products during oxygen-limited growth on glucose in chemostat cultures. None of these fermentation products were produced in oxygen-limited chemostat cultures grown on sucrose and the fraction of the sucrose that could not be respired remained unused in the culture medium. This absence of alcoholic fermentation was not due to repression of the key fermentative enzymes pyruvate decarboxylase and alcohol dehydrogenase. In contrast to some other yeasts that exhibit a Kluyver effect, D. yamadae did not exhibit a preference for ethanol in batch cultures grown on mixtures of ethanol and sucrose. Sucrose metabolism in D. yamadae involves intracellular hydrolysis by an alpha-glucosidase. Incubation of weakly buffered cell suspensions with sucrose led to a rapid transient alkalinization, indicating the presence of a sucrose-proton symport system. The apparent substrate saturation constant of the sucrose-uptake system was 0.2 mmol l-1. Sucrose-dependent alkalinization rates were much lower in samples from oxygen-limited cultures than in samples from aerobic cultures. Transient responses of D. yamadae to oxygen limitation were investigated by applying a sudden decrease in the oxygen feed to aerobic sugar-limited chemostat cultures. In glucose-grown cultures, this led to alcoholic fermentation and no significant accumulation of sugar occurred after the switch. In sucrose-limited cultures, sugar accumulation occurred instantaneously after the switch, and ethanol formation was virtually absent.(ABSTRACT TRUNCATED AT 250 WORDS)
TL;DR: Except at low glutamine and low oxygen levels, the specific death rate of the cultures was found to decrease with increasing dilution rate (D), which suggests that cell death was due to a non‐growth‐linked inhibitory product of the cells.
Abstract: In the present study, the steady-state cell density (X) of chemostat cultures of murine hybridoma was varied by the concentration of glucose and glutamine in culture medium and the dissolved oxygen partial pressure. Except at low glutamine and low oxygen levels, the specific death rate (k(d)) of the cultures was found to decrease with increasing dilution rate (D). However, the plot of k(d) vs. X/D yielded linear relation, which suggests that cell death was due to a non-growth-linked inhibitory product of the cells. The k(d) value measured at low glutamine and low oxygen levels remained practically unchanged over a wide range of D between 0.020 and 0.029 h(-1). The k(d) for low oxygen cultures was always lower than the values obtained in low glucose and low glutamine cultures. A low-molecular-weight component of possibly less than 3000 MW was detected to be cell-death-inducing in the supernatant of exponentially growing cultures. It was neither lactate nor ammonium. The autoinhibitor was not cell-line specific. (c) 1995 John Wiley & Sons, Inc.
TL;DR: The influence of growth rate and oxygen availability on siderophore, protease, and lipase production in Burkholderia cepacia was assessed and demonstrated the opposite trend.
Abstract: The influence of growth rate and oxygen availability on siderophore, protease, and lipase production in Burkholderia cepacia was assessed for cells grown in a chemostat under iron limitation. Whereas siderophore and protease production increased with growth rate and oxygen yet decreased under oxygen depletion, lipase production demonstrated the opposite trend.
TL;DR: Results indicate that trehalose plays a growth rate dependent role in the tolerance of S. cerevisiae to acetic acid.
Abstract: The effects of acetic acid and specific growth rate on acetic acid tolerance and trehalose content of Saccharomyces cerevisiae CBS 2806 were studied using anaerobic chemostat cultures. Cells grown in the presence of acetic acid at a defined specific growth rate showed a higher acetic acid tolerance and a slightly lower trehalose content. Cells grown at a low specific growth rate showed a lower energy demand, a higher acetic acid tolerance, and a higher trehalose content. These results indicate that trehalose plays a growth rate dependent role in the tolerance of S. cerevisiae to acetic acid.
TL;DR: With glucose-limited continuous cultures of Petunia hybrida six steady states were obtained at specific growth rates varying from 0.012 h(-1) (corresponding with culture residence times varying from 285 to 85 h), and the macromolecular and the elemental biomass composition showed no major differences over the range of growth rates examined.
Abstract: With glucose-limited continuous cultures of Petunia hybrida six steady states were obtained at specific growth rates varying from 0.0035 to 0.012 h−1 (corresponding with culture residence times varying from 285 to 85 h). The macromolecular and the elemental biomass composition which were determined in four steady states showed no major differences over the range of growth rates examined. During all six steady states specific subtrate and oxygen consumption as well as biomass and extracellular product formation rates were monitored. Moreover the specific activities of the mitochondrial cytochrome and alternative pathway were determined and used to estimate specific adenosine triphosphate (ATP) production rates. Data thus obtained were used in the determination of maintenance and true growth yield parameters. For the maintenance on glucose and ATP values of 0.0070 C-mol/C-mol/h and 0.034 mol/C-mol/h were obtained, respectively. True yields of biomass on glucose and ATP were 0.50 C-mol/C-mol and 0.28 C-mol/mol, respectively. © 1995 John Wiley & Sons, Inc.
TL;DR: A non-structured Monod-type equation, describing the relation between specific growth rate and specific extracellular-inulinase production rate, was used to fit experimental data and adequately described biomass production in the fed-batch culture.
TL;DR: For one of the resources it is shown that, while moderate enrichment can be beneficial, sufficient enrichment leads to the extinction of the microbial population, and for the other resource, enrichment leads from washout or initial condition dependent outcomes to survival, and is thus beneficial.
Abstract: A model of single-species growth in the chemostat on two non-reproducing, growth-limiting, noninhibitory, perfectly substitutable resources is considered. The medium in the growth vessel is enriched by increasing the input concentration of one of the resources. Analytical methods are used to determine the effects of enrichment on the asymptotic behaviour of the model for different dilution rates. It is shown that there exists a threshold value for the dilution rate which depends on the maximal growth rate of the species on each of the resources. Provided the dilution rate is below the threshold, enrichment is beneficial in the sense that the carrying capacity of the environment is increased, regardless of which resource is used to enrich the environment. When the dilution rate is increased beyond the threshold, it becomes important to consider which resource is used for enrichment. For one of the resources it is shown that, while moderate enrichment can be beneficial, sufficient enrichment leads to the extinction of the microbial population. For the other resource, enrichment leads from washout or initial condition dependent outcomes to survival, and is thus beneficial. There are important implications of these results to the management of natural aquatic ecosystems. For example, while enrichment may be beneficial to the microbial species during the summer months, it can lead to their decimation during spring run-off, when the natural dilution rate is higher.