Showing papers on "Chemostat published in 1986"

Growth yields of Desulfotomaculum orientis with hydrogen in chemostat culture

Abstract: Desulfotomaculum orientis (strain Singapore 1) was grown autotrophically with H2+CO2 and sulfate, thiosulfate or sulfite as electron acceptor in sulfide- and pH-controlled continuous culture. Under sulfate-limiting conditions real growth yields of up to 9.7 g cell dry mass per mol sulfate were obtained. Electron acceptor limitation resulted in the excretion of up to 14.5 mmol acetate per liter, formed by reduction of CO2 with H2. Acetate production was not coupled to an increase of growth yields: under hydrogen-limiting conditions only 1.6 mmol acetate per liter was produced, and even higher growth yields of up to 12,4 g cell dry mass per mol sulfate were obtained. With thiosulfate or sulfite as electron acceptor growth yields increased up to 17.9 g cell dry mass per mol electron acceptor. Growth yields were not simply correlated with the growth rate, and did not allow the determination of maintenance coefficients and the extrapolation to maximal yields at infinite growth rate (Ymax). The maximal growth rates (μmax) with sulfate and thiosulfate were 0.090 and 0.109 h-1, respectively, if cells were grown continuously in sulfidostat culture under nonlimiting conditions.

Effect of Growth Conditions on the Production, Composition and Viscosity of Xanthomonas campestris Exopolysaccharide

Abstract: Summary: A streptomycin-resistant variant of Xanthomonas campestris was grown in defined nutrient-deficient media in both batch and continuous culture. The production, composition and viscosity of the extracellular polysaccharide (xanthan) synthesized by this strain were influenced by the fermentation time and nutrient exhaustion in batch culture and by the dilution rate in continuous culture. The specific rate of exopolysaccharide synthesis was maximal during exponential growth in all of the nutrient-deficient media studied although some xanthan was formed during stationary phase. The concentration of exopolysaccharide decreased at later stages of stationary phase in some cultures. Both the extent of acylation and the consistency index of xanthan isolates were low or minimal during exponential growth, maximal in polysaccharide isolated as the growth rate fell and usually lower after this time. Between dilution rates of 0·03 and 0·06 h−1 in chemostat culture, the cell and exopolysaccharide dry weights were independent of dilution rate, the specific rate of xanthan synthesis decreasing at lower growth rates. Although the variation in the acyl content and consistency index was less than that observed in batch culture, exopolysaccharide isolated at higher dilution rates tended to have a higher acetyl content, lower pyruvyl content and lower consistency index.

Continuous cultivation of recombinant Escherichia coli: Existence of an optimum dilution rate for maximum plasmid and gene product concentration.

Abstract: Growth yield factors, plasmid stability, cellular plasmid content, and cloned gene product activity for Escherichia coli HB101 containing plasmid pDM246 were measured at several dilution rates in continuous culture. Cell mass yield per mass of glucose consumed declined with increasing dilution rate. There was no evidence of plasmid segregational instability in any experiments, none of which employed selective medium. Plasmid content per cell varied with population-specific growth rate as observed in earlier batch experiments with the same strain. Plasmid content declined with increasing specific growth rate following indication of a maximum number of plasmids per cell at specific growth rates of ca. 0.3 h−1. Cloned gene product (β-lactamase) activity exhibited a sharp maximum with respect to dilution rate in continuous culture. Qualitatively different results were observed in previous experiments in batch cultivation in which specific growth rate changes were effected by altering medium composition.

Simultaneous utilization of methanol-glucose mixtures by Hansenula polymorpha in chemostat: Influence of dilution rate and mixture composition on utilization pattern.

Abstract: The utilization of mixtures of methanol (C,) and glucose (c6) of different composition by the methylotrophic yeast Hansenula polyrnorpha was studied in carbon-limited chemostat culture. For all mixtures tested a similar utilization pattern was observed: At low dilution rates both carbon sources were utilized simultaneously, but at high dilution rates the cells used glucose only and the unutilized methanol accumulated in the culture medium. When grown with C1 only, the cells exhibited a critical dilution rate Dc(Cl) of 0.19 h-’, but when Cl-c6 mixtures were used as the carbon and energy substrate, the yeast was able to completely utilize C1 at dilution rates considerably higher than Dc(Cl). The dilution rate at which the transition from c,-c6 growth to c6 growth occurred (D,) was strictly dependent on the composition of the Cl-c6 mixture in the feed, and 0, increased with decreasing proportions of C, in the mixture. During mixed substrate growth the formation of biomass from the two substrates was additive. The results reported indicate that the utilization of Cl-c6 mixtures and hence D, in H. polyrnorpha are subject to two different regulatory regimes. When the cells were growing with Cl-c6 mixtures containing more than 60% cl, the transition form Cl-c6 to c6 growth was most probably influenced by the maximum C1 oxidizing capacity of the cells, whereas for growth with mixtures containing less than 40% C1, a growth rate of 0.28-0.30 h - seemed to be the limiting barrier for the simultaneous utilization of the components of the binary carbon and energy substrate mixture.

Fitness as a function of β-galactosidase activity in Escherichia coli

Abstract: Chemostat cultures in which the limiting nutrient was lactose have been used to study the relative growth rate of Escherichia coli in relation to the enzyme activity of β-galactosidase. A novel genetic procedure was employed in order to obtain amino acid substitutions within the lacZ-encoded β-galactosidase that result in differences in enzyme activity too small to be detected by ordinary mutant screens. The cryptic substitutions were obtained as spontaneous revertants of nonsense mutations within the lacZ gene, and the enzymes differing from wild type were identified by means of polyacrylamide gel electrophoresis or thermal denaturation studies. The relation between enzyme activity and growth rate of these and other mutants supports a model of intermediary metabolism in which the flux of substrate through a metabolic pathway is represented by a concave function of the activity of any enzyme in the pathway. The consequence is that small differences in enzyme activity from wild type result in even smaller changes in fitness.

Nitrogen fixation in molybdenum-deficient continuous culture by a strain of Azotobacter vinelandii carrying a deletion of the structural genes for nitrogenase (nifHDK).

Abstract: Steady-state chemostat cultures of Azotobacter vinelandii strain CA11, carrying a deletion of genes encoding the structural polypeptides of nitrogenase nifHDK, were established in a simple defined medium chemically purified to minimize contamination by Mo. The medium contained no utilizable N source. Growth was dependent on N2 (1.1 X 10(8) viable cells X ml-1 at D = 0.176 h-1), and was inhibited by Mo (20 nM). DNA hybridization showed the deletion to be stable during prolonged (55 days) growth in the chemostat (132 doublings). Since batch cultures, using unsupplemented 'spent' chemostat medium, showed good growth (1.9 X 10(8) cells X ml-1), no requirement for subnanomolar concentrations of Mo was found. The biomass yield, as the dilution rate (D) was varied, showed that the N content of the culture, protein and dry wt. increased as D was decreased, indicating that neither N2 nor O2 were limiting growth. The limiting nutrient was not identified. Substantial amounts of H2 were evolved by the chemostat cultures, probably as the result of inhibition of O2-dependent hydrogenase activity by nitrilotriacetic acid present in the medium. Over a range of D values approx. 50% of the electron flux through the alternative system was allocated to H+ reduction. C2H2 was a poor substrate, being reduced at 0.14-0.1 times the rate of N2 fixation, calculated from the N content of the cells. SO4(2-)-limited steady-state continuous cultures of strain UW136 (wild-type for nifHDK) had a 2-fold greater biomass in the presence of MoO4(2-) (1 microM). The significance of this finding for 'Mo-limited' continuous cultures [Eady & Robson (1984) Biochem. J. 224, 853-862] is discussed.

Influence of the Carbon: Nitrogen Ratio of the Growth Medium on the Cellular Composition and the Ability of the Methylotrophic Yeast Hansenula polymorpha to Utilize Mixed Carbon Sources

Abstract: Summary: The methylotrophic yeast Hansenula polymorpha was grown in a chemostat with a medium containing a mixture of glucose (C6) and methanol (C1) (87·8% C6: 12·2% C1, w/w) as sole carbon source and NH4 + as sole nitrogen source. At a constant growth rate (D 0·10 h-1) the influence of the carbon: nitrogen ratio (C:N) of the inflowing medium on the cellular and enzymic composition of the cells was studied. Three distinct growth regimes were recognized. A medium with a C:N ratio 31 resulted in nitrogen-limited growth (low protein but high carbohydrate content of the cells) and the cells metabolized only glucose. A transition growth regime was observed during growth on media with intermediate C:N ratios (12 31). When assessed from both substrate consumption and cellular composition, growth was double-substrate (carbon and nitrogen)-limited. In this transition growth regime, changes in carbon metabolism and the cellular and enzymic composition of the cells were found. With increasing C:N ratios in the growth medium a gradual repression of the synthesis of methanol-assimilating and dissimilating enzymes was found. This effect was most pronounced for alcohol oxidase, and as a consequence the cells switched from the utilization of the carbon substrate mixture to growth on glucose alone. The data presented suggest that the range within which double-substrate-limited growth can be expected is predictable from the composition of cells grown under single substrate limitation.

Modeling of microbial substrate conversion, growth and product formation in a recycling fermentor.

Abstract: Paracoccus denitrificans and Bacillus licheniformis were grown in a carbon- and energy source-limited recycling fermentor with 100% biomass feedback. Experimental data for biomass accumulation and product formation as well as rates of carbon dioxide evolution and oxygen consumption were used in a parameter optimization procedure. This procedure was applied on a model which describes biomass growth as a linear function of the substrate consumption rate and the rate of product formation as a linear function of the biomass growth rate. The fitting procedure yielded two growth domains for P. denitrificans. In the first domain the values for the maximal growth yield and the maintenance coefficient were identical to those found in a series of chemostat experiments. The second domain could be described best with linear biomass increase, which is equal to a constant growth yield. Experimental data of a protease producing B. licheniformis also yielded two growth domains via the fitting procedure. Again, in the first domain, maximal growth yield and maintenance requirements were not significantly different from those derived from a series of chemostat experiments. Domain 2 behaviour was different from that observed with P. denitrificans. Product formation halts and more glucose becomes available for biomass formation, and consequently the specific growth rate increases in the shift from domain 1 to 2. It is concluded that for many industrial production processes, it is important to select organisms on the basis of a low maintenance coefficient and a high basic production of the desired product. It seems less important that the maximal production becomes optimized, which is the basis of most selection procedures.

Effect of pH oscillations on a competing mixed culture.

Abstract: Two microorganisms, E. coli and S. cerevisiae, competing for glucose were maintained in a stable cycle of coexistence by alternating the growth advantage between the two organisms by oscillating the pH in a Chemostat. Pure culture experiments found S. cerevisiae to be insensitive to pH between 5 and 4.3 with a maximum specific growth rate (micro(max)) of 0.4/hr; while micro(max) of E. coli decreased from 0.6 h(-1) at pH 5 to 0.1 h(-1) at pH 4.3. Steady-state and cross-inoculation chemostat runs at a dilution rate of 0.17 h(-1) confirmed the expectation that the mixed culture system is unstable at constant pH with E. coli dominating at pH 5 and S. cerevisiae dominating at pH 4.3. Three pH oscillation experiments were performed at D =0.17 h(-1) with 1 g per liter glucose feed. The 16 h/16 h cycle was stable for six periods with a stable alternating cycle of E. coli and S. cerevisiae being quickly established. A 18 h pH 5/14 h pH 4.3 cycle was found to be stable with smaller yeast concentrations. A 6 h/6 h cycle was found unstable with yeast washout. Simulation results were compared with these runs and were used to predict the onset of instability. Oscillations of pH can force stable persistence of a competing mixed culture that is otherwise unstable. Thus, varying conditions are experimentally demonstrated to be one explanation for competitive coexistence.

Utilization of poly-β-hydroxybutyrate in free-living cultures of Rhizobium ORS571

Abstract: The effect of carbon starvation on growth and poly-β-hydroxybutyrate (PHB) utilization in oxygen-limited chemostat cultures of Rhizobium ORS571 was studied. Under oxygen-limited growth conditions PHB was not degraded. When in a nitrogen-fixing oxygen-limited culture, after stopping the medium supply, the dissolved oxygen concentration was maintained at 10 μM, a slow breakdown of PHB was observed. Addition of ammonia and air to a nitrogen-fixing oxygen-limited culture after the medium supply had been stopped, resulted in the simultaneous utilization of PHB and succinate. The possible use of the energy derived from PHB degradation in Rhizobia bacteria and bacteroids is discussed.

Growth of Hyphomicrobium ZV620 in the Chemostat: Regulation of NH+4-assimilating Enzymes and Cellular Composition

Abstract: Summary: The regulation of the NH+ 4-assimilating enzymes glutamate dehydrogenase (GDH), glutamine synthetase (GS) and glutamate synthase (GOGAT), and the cellular composition of Hyphomicrobium ZV620 grown in a chemostat with methanol and NH+ 4 as the supplied C- and N-sources were investigated. The influence of either C- or N-limitation (as a function of dilution rate) and of the C: N ratio (at a constant growth rate) was studied. NADP+-dependent GDH was active at high NH+ 4-concentrations and was repressed at low NH+ 4-concentrations. The activity increased with increasing dilution rates under C-limited growth conditions. Derepression of NADP+-dependent GDH was observed at low dilution rates under N-limited growth conditions. GS was more active at low NH+ 4-concentrations where both the total enzyme level (deadenylylated plus adenylylated forms) and the active fraction increased. C-limited growth resulted in low activities of GS, whereas activity in N-limited cells was consistently high. Dilution rate did not have a significant influence on the specific activity. The specific activity of GOGAT increased with decreasing NH+ 4 concentrations. Under both C- and N-limitation the specific activity of GOGAT increased with increasing growth rates. The C-content of the cells changed very little under the various growth conditions tested. The N-content and the protein content of the cells did not alter under C-limitation. N-limited growth conditions caused the cells to accumulate poly β-hydroxybutyrate. As a consequence, both the N-content and the protein content of the cells decreased.

Acidogenic fermentation of protein/carbohydrate mixtures by bacterial populations adapted to one of the substrates in anaerobic chemostat cultures

Abstract: The influence of the adaptation procedure on the simultaneous fermentation of glucose and gelatin by putatively carbon-limited mixed anaerobic bacterial populations was investigated. In one series of experiments glucose, dissolved in a mineral salts solution, was fed to mixed populations of bacteria in anaerobic carbon-limited chemostat cultures maintained at different pH values and at 30°C. When, after reaching a steady state, the carbon substrate was switched to gelatin, growth ceased. However, when gelatin was added to the medium as a second carbon substrate, it was found in all cases that hydrolysis and fermentation of the protein proceeded to a limited extent (<30%) and that glucose continued to be completely metabolized. In a second series of experiments, bacterial populations were adapted to gelatin under comparable experimental conditions. After reaching a steady state, glucose was added to the medium as a second carbon substrate. Following establishment of the new steady state it was found that hydrolysis of gelatin was not inhibited but its fermentation was. It is concluded that anaerobic bacterial populations can loose their ability to degrade a protein substrate, depending on the adaptation procedure.

Kinetics and energetics of reduced sulfur oxidation by chemostat cultures of Thiobacillus ferrooxidans

Abstract: Thiobacillus ferrooxidans was grown in chemostat cultures with thiosulfate and tetrathionate as the limiting substrates. The yields at steady state on both substrates at different dilution rates were calculated. In a few experiments the air supply was supplemented with 2% CO2 (v/v). This resulted in a slightly increased yield. Cells from the chemostat cultures were used to study the kinetics of thiosulfate, tetrathionate, sulfite and sulfide oxidation. With all substrates mentioned the Ks values were in the micromolar range. The values for thiosulfate and tetrathionate were 2 orders of magnitude lower that those published previously.

Analysis of protein and cell volume distribution in glucose-limited continuous cultures of budding yeast

Abstract: Method of flow cytometric analysis have recently been developed that make it possible to obtain segregated data on a single cell basis. In particular, it has been previously demonstrated that protein distributions obtained by flow cytometry give information about the law of growth of the cell population and the law of growth of the single cell; thus these distribution show how the microbial population is actually growing at the moment of the analysis and may yield more accurate and predictive information. We have extended the analysis of protein distribution and cell volume distribution to continuous cultures of Saccharomyces cerevisiae growing in a glucose-limited chemostat. We have found that: (1) to each dilution rate corresponds a given protein and volume distribution that does not change with time in steady state cultures; (2) there is a good proportionality between the average cell volume and the average protein content; (3) the protein distribution obtained can be easily analyzed with the model of growth of yeast previously developed in our laboratory; (4) the analysis of perturbed states shows that both protein distribution and volume distribution change very quickly; thus they are very sensitive parameters and can be used for monitoring and controlling industrial fermentation.

Activity, death and lysis during microbial growth in a chemostat

Abstract: The significance of death and lysis processes during microbial growth in chemostat cultures is discussed. A structured model is developed to describe such processes and the model is partially verified for carbon limited chemostat cultures of Klebsiella pneumoniae. It seems probable that death and lysis are coincident, when non-viable cells are not considered to be dead.

Mathematical investigations of growth of microorganisms in the gradostat

Abstract: Microbial ecosystems with spatial distribution of substrate (nutrient) supply in the form of gradients have been studied in a laboratory system called the gradostat, which is a series of coupled chemostats. We investigate analytically and numerically a mathematical model, similar to the one for a single chemostat based on Michaelis-Menten kinetics, of the growth of one species of microorganisms in the gradostat in the presence of one limiting substrate and two limiting complementary substrates. Our analysis predicts various patterns of spatial distribution of microorganisms at steady state and suggests further experiments to be performed with the gradostat.

The stability of the yeast plasmid pJDB248 depends on growth rate of the culture

Abstract: The stability of the plasmid pJDB 248 has been measured in theS. cerevisiae strain S150-2B growing in a chemostat under conditions of glucose limitation. It was found that reducing the growth rate of the culture led to a more rapid loss of the plasmid from the cells.

A mathematical model of syntrophic cocultures in the chemostat

Abstract: A model is presented for syntrophic associations between H2-producing acetogenic bacteria and H2-utilizing bacteria. A growth rate expression different from the usual Monod equation is applied to the H2-producing acetogenic bacterium to take into account the thermodynamics of the metabolic reaction involved as dominant factor. The steady of states of the model system are given as branches in a bifurcation diagram. Numerical experiments on the stability of the branches and on the influence of different values in model parameters are performed. The predictions of our model are discussed with regard to the results obtained from experiments with syntrophic cocultures of different species of H2-producing acetogenic bacteria in combination with H2-consuming bacteria.

Lipid formation by Cryptococcus albidus in nitrogen-limited and in carbon-limited chemostat cultures

Abstract: Cryptococcus albidus var. Albidus CBS 4517 was grown in nitrogen-limited and in carbon-limited chemostat cultures. The effect of growth rate and limiting nutrient on lipid accumulation and fatty acid composition was investigated. The maximum lipid content in the biomass was, in both cultivation systems, observed at the lowest dilution rate (growth rate) tested. At this dilution rate, D=0.31 h-1, cells from the nitrogen-limited culture contained 41% (w/w) lipid and cells from the carbon-limited culture 37%. These results indicate the ability of C. albidus, unlike other oleaginous yeasts, to accumulate lipid also in carbon-limited chemostats. The yield of lipid from carbon source was about the same at D=0.031 h-1 in nitrogen-limited (Y L/S=0.16 g/g) as in carbon-limited (Y L/S=0.17 g/g) cultures and decreased with increasing growth rates. In the nitrogen-limited culture, the lipid productivity was about constant at low growth rates (0.031–0.056 h-1) and a slight decrease was observed at D=0.08 h-1, while the specific lipid productivity, q L, increased to 27.5 mg/g per hour. In the carbon-limited culture, however, lipid productivity increased with increasing growth rates and reached its maximum value near μmax, whereas q L was about constant at 20 mg/g per hour. The fatty acid composition was influenced by the specific growth rate in nitrogen-limited as well as in carbon-limited cultures, although the changes were more pronounced during carbonlimitation. A decrease in the degree of unsaturation (Δ/mole) was also observed with increasing lipid content in the cells.

Coexistence of S. cerevisiae and E. coli in chemostat under substrate competition and product inhibition.

Abstract: A mixed culture of Saccharomyces cerevisiae and Escherichia coli was established in a stable coexistence steady state in a chemostat under constant operating conditions. The species competed for glucose, the growth-limiting resource, and produced acetate and ethanol. The acetic acid was shown to be very inhibitory to E. coli in pure culture at pH 5 while ethanol inhibition was only marginal. No significant inhibition of S. cerevisiae growth was observed by either acetate or ethanol. Pure culture parameters were measured and used in the analysis. Linearized stability analysis for the case when both organisms produce the inhibitor showed that a transition through three stable outcomes was possible as the feed concentration is lowered. Experimental studies verified these predictions, and successive transitions from a yeast growth steady state, to a coexistence steady state, and to an E. coli growth steady state were obtained by lowering the glucose concentration in the feed from 10 to 5 to 2.5 g/l respectively. This dynamic behavior is distinct from the outcomes of other competition-inhibition combinations and experimentally demonstrates for the first time that coexistence is possible due to substrate competition and product inhibition. 30 references.

The effect of pH on the growth and metabolism of Streptococcus bovis in continuous culture.

Abstract: Streptococcus bovis H13/1 was grown anaerobically at pHs between 5.0 and 6.5 in a glucose-limited chemostat at a dilution rate of 0.05/h. The growth yield and the production of acetate, ethanol and formate decreased at pHs less than 6.5 whereas the production of lactate increased at the lower pH values. When a culture was subjected to sequential pH changes, growth yield and fermentation products were influenced not only by the pH existing in the culture medium but also by the metabolic activity of the cells at the preceding pHs in the sequence. The results are discussed in relation to the mechanisms available for the maintenance of pH homeostasis and for the metabolic control of fermentation pathways in Strep. bovis.

The effect of the dissolved oxygen concentration and anabolic limitations on the behaviour of Rhizobium ORS571 in chemostat cultures

Abstract: Chemostat cultures of Rhizobium ORS571 limited by the supply of oxygen or an anabolic substrate contained poly-β-hydroxybutyrate (PHB). Low amounts of PHB (about 10%) were present in ammonia- or nitrate-limited cultures; higher amounts were found in Mg++-limited cultures (about 20%) and in oxygen-limited nitrogen-fixing cultures (37%). A method is described to calculate YATP values (g PHB-free biomass · mol-1 ATP) from the Ysucc values (g dry wt·mol-1 succinate) measured. Ysucc and YATP values in cultures limited by the supply of an anabolic substrate and in the oxygen-limited ammonia-assimilating culture were much lower than the values found in the PHB-free succinate-limited cultures. This shows that uncoupling of growth and energy production occurred. Therefore, H2/N2 ratio (mol hydrogen formed per mol nitrogen fixed) in nitrogen-fixing cultures could not be calculated from the comparison of the YATP value found in the nitrogen-fixing culture and the value found in the corresponding ammonia-assimilating culture.

Effect of growth temperature on the morphology and performance of Zymomonas mobilis ATCC 29 191 in batch and continuous culture

Abstract: Increasing the temperature in chemostat culture ofZymomonas mobilis ATCC 29 191 with low and high glucose concentrations was found to result in a decreasing frequency of septation leading to the formation of long filaments and in increasing outer membrane blebbing. Whether this effect is strain specific or universal inZymomonas is, unknown. Improvements in the fermentation kinetics could be achieved at elevated temperatures, with an optimum at 33°C. Temperatures >30°C induced “uncoupled growth” in chemostat cultures ofZ. mobilis ATCC 29 191. The results of this study emphasize the importance of temperature regulation in optimizing the performance of continuous fermentations withZymomonas.

Growth rate dependent optimum ratios in selenastrum minutum (chlorophyta): implications for competition, coexistence and stability in phytoplankton communities

Abstract: Steady-State growth equations predict that the optimum C:P ratio (R) of Selenastrum minutum (Naeq.) Collins should change by a factor of 20 over the growth range of this organism. Chemostat cultures were established at fixed inflow C:P ratios chosen such that a transition from carbon to phosphorus limitation should occur solely as a result of increasing the steady-state growth rate. Measurements of residual dissolved inorganic carbon (DIC), cellular C:P, the kinetics of photosynthesis with respect to [DIC] and the response of culture biomass lo DIC or K2HPO4 additions were obtained. These results show that optimum ratios are growth rate dependent and that this dependency can be predicted based on steady-stale algal growth equations. A theoretical analysis was undertaken evaluating the range of growth rate dependent changes in the optimum ratio which could be expected for different nutrient pairs. Further analysis showed that, under certain conditions, the growth rate dependence of the optimum ratio may alter the breadth of zones of stable coexistence between species and allow for either the formation or complete elimination of such zones.

Formaldehyde Production by Cells of a Mutant of Candida boidinii S2 Grown in Methanol-limited Chemostat Culture

Abstract: Formaldehyde production was investigated with cells of a mutant, AOU-1, of a methanol yeast, Candida boidinii S2 grown in methanol-limited chemostat culture. The highest productivity was shown with cells from the culture at a dilution rate of 0.075 hr-1, when cells had the highest activity of alcohol oxidase and almost minimum activity of formaldehyde dehydrogenase. Under optimal reaction conditions, 950 mm formaldehyde was produced in 10-hr reaction with the cells. By the chemostat culture, not only formaldehyde productivity but also cell productivity was improved in comparison with batch culture. A maximum cell productivity of 0.2 g · liter-1 · hr-1 and a cell yield of 47% were obtained.

Directed selection of differentiation mutants of Streptomyces noursei using chemostat cultivation.

Abstract: A nourscothricin-producing Streptomyces noursei strain was continuously cultivated in a chemostat equipped with a stirrer for mechanical fractionation of the mycelium Different cultivation conditions allowed the selection of six types of differentiation mutants after the culture had reached a population genetically stationary state The mutants showed an altered control pattern of sporulation as well as altered antibiotic biosynthesis and antibiotic resistance In addition, the stability of the recombinant plasmid pIJ385 in several differentiation type mutants as host strains was tested The results suggest that there exists a strong correlation between the cultivation conditions employed and the type of differentiation mutants selected