Effect of Growth Rate on the Synthesis of Penicillin by Penicillium chrysogenum in Batch and Chemostat Cultures

The kinetics of penicillin production by Penicillium chrysogenum Wis 54-1255 in a glucose-limited chemostat and in batch cultures are reported. The specific production rate of penicillin, q(pen) (units per milligram of dry weight per hour) was independent of specific growth rate over the range 0.014 to 0.086 hr. Growth was stopped by restricting the glucose supply to the "maintenance ration," that is, the glucose requirement of the organism at zero growth rate with all other nutrients in excess. Under such conditions, the organism dry weight remained constant, but the q(pen) fell approximately linearly to zero at a rate inversely related to the previous growth rate. Glucose supplied in excess of the maintenance ration inhibited the decay of q(pen). At a critical growth rate between 0.009 and 0.014 hr, the decay was completely inhibited. Quantitative expressions for the q(pen) of growing and nongrowing cultures were derived and used to predict the steady-state concentrations of penicillin accumulating in one- and two-stage continuous processes. A rational explanation of the kinetics of penicillin accumulation in batch cultures is given, relating the rate of penicillin synthesis to growth rate. It is concluded that an important role of corn steep liquor (CSL), a heterogeneous carbon and nitrogen source commonly used in penicillin production media, is the provision of substrates which allow a high concentration of mold to be reached before the growth rate falls below the critical value. CSL had no significant effect on q(pen).

Molecular mimicry and ankylosing spondylitis: possible role of a novel sequence in pullulanase of Klebsiella pneumoniae

Molecular mimicry has been shown between two sequences of Klebsiella pneumoniae pulD secretion protein (DRDE) with HLA-B27 (DRED) and pulA (pullulanase) enzyme (Gly-X-Pro) with types I, III and IV collagen respectively. IgG antibody levels in AS patients were elevated against 16mer synthetic peptides of HLA-B27 and pulD by enzyme immunosorbent assay (ELISA) compared to controls (P < 0.001). ELISA assays against K. pneumoniae grown in the absence and presence of pullulan demonstrated significant levels of IgA antibody in AS patients compared to controls (P < 0.001). Increased IgA and IgG antibody levels to pulA and types I and IV collagen were observed in AS patients compared to controls (P < 0.001). These observations could be relevant in the sequence of molecular events in AS.

Maintenance energy: a general model for energy-limited and energy-sufficient growth

The new model proposed to account for the energy requirement for growth includes both a constant maintenance energy term (m) independent of the specific growth rate and a term (m') which decreases linearly with increase in specific growth rate and becomes zero at the maximum specific growth rate. The available data for testing the model do not deviate significantly from the relations predicted. Consistent values of the maximum growth yield (YG) can be derived, irrespective of whether the cultures are energy limited or energy sufficient. Attention is drawn to the possibility that the constant maintenance energy term may be estimated from the maximum specific growth rate.

Conversion of glucose to fatty acids and methane: roles of two mycoplasmal agents

Two species of obligately anaerobic mycoplasmas were the major components of a methanogenic glucose-limited enrichment culture. In pure culture, one of these organisms, tentatively named Anaeroplasma sp. strain London, was shown to be responsible for the fermentation of glucose to fatty acids, hydrogen, and carbon dioxide; the other mycoplasma was shown to produce methane from hydrogen and carbon dioxide and was named Methanoplasma elizabethii. This same methanogenic mycoplasma contained a low-molecular-weight fluorescent cofactor which had a maximum light absorbance at 430 nm. When both species of mycoplasmas were grown together on glucose, fermentation products included fatty acids and methane. For the first time, mycoplasmas are implicated as agents of anaerobic degradation and methanogenesis in a sewage sludge digester.

Growth of human diploid cells (strain MRC-5) in defined medium; replacement of serum by a fraction of serum ultrafiltrate

A calf serum ultrafiltrate fraction permitted growth for at least 3.5 generations, including one subculture, of MRC-5 cells in defined medium in the absence of whole serum. The active material has a molecular weight of 10 000 Daltons or less. This suggests that there may be no requirement for a large macromolecular component of serum. The ultrafiltrate was assayed by maximum cell yield from a serum-limited inoculum in a defined medium containing non-limiting amounts of vitamins, amino acids, glucose, a 68-component supplement, iron and methylcellulose. The levels of vitamins, amino acids and glucose were based on quantitative measurements of uptake and the levels of the other components by minimum amount required for maximum yield in defined medium without ultrafiltrate or serum. With excess ultrafiltrate maximum cell yield was limited by the defined part of the medium, probably the supplement. The cell doubling time in defined medium with ultrafiltrate fractions was 70 h compared with 27 h in the medium with serum. Excess ultrafiltrate did not inhibit growth. The lowered growth rate is attributed to a nutritional deficiency in the supplement.

Biomass yields of Chlorella from iron (Yx/Fe) in iron-limited batch cultures

The maximum biomass in iron-limited photosynthetic batch cultures of chlorella increased as the logarithm of the iron concentration. The growth yield from iron (UxFe) showed a marked inverse relation to the specific growth rate. The maximum biomass yield, g dry biomass/g iron consumed, was 7.5 X 10(3) with specific growth rate 0.108h-1; the minimum was 0.79 X 10(3) with specific growth rate 0.145 h-1. The maximum specific growth rate in the exponential phase of Fe limited cultures varied as the initial Fe concentration. Fe-limited growth made the cells adhere to a glass surface.

Development of the agar disk method for the rapid selection of cephalosporin producers with improved yields

To screen the abilities of mutant strains of Cephalosporium to produce cephalosporin C, colonies of the organism were grown on the surface of small (4-mm diameter) disks of agar medium. After incubation of the disks for periods of up to 5 days, the antibiotic contents of the disks were assayed by placing them on agar plates of the assay organism and determining the diameters of the inhibition zones. The amount of nitrogen source in the agar disk medium was used to control the amount of antibiotic produced in the disk and, thus, the sensitivity of screening. The relation of agar disk inhibition zone diameters to log shake-flask titers was linear with short incubation times (2 to 3 days) of the disks, but shifted towards a higher order with prolonged incubation (4 to 5 days). The optimum incubation time for the disks was 4 to 5 days, and then a 15% difference in zone diameters was significant with 10 disks per sample. The minimum difference between the shake-flask titers, which could be detected by the agar disk method with 10 disks per sample, was about 30% with 5 days of incubation for the disks. The results suggest that the shake-flask culture underestimated the degree of improvement in strain productivity.

Nutrition and factors limiting the growth of a methanogenic bacterium (Methanobacterium thermoautotrophicum)

The purification of Methanobacterium thermoautotrophicum from a culture contaminated with a heterotrophic organism is described. A defined inorganic medium under H2/CO2 (80:20 v/v) has been developed to support growth of M. thermoautotrophicum up to a concentration of at least 1.7 g dry weight/l. In a conventional medium iron and nitrogen sources were found to be growth-limiting factors. Throughout most of the culture period the rate of transfer of hydrogen or carbon dioxide from gas to liquid was the factor which controlled the growth rate. The growth yields of bacteria were in the range of 0.6-1.6 g dry weight/mole CH4.

The nutrient requirements of MRC-5 human diploid cells

Nutrients were assayed by their effect on maximum cell yield (maximum cell population less inoculum) of MRC-5 cells previously maintained in Eagle's basal medium with 10% (v/v) serum, trypsinised, centrifuged and washed. When nonlimiting amounts of iron, methylcellulose and a 68-component supplement were included in our defined medium, cell yields obtained were equivalent to those obtained with 2 to 3% whole serum. Growth then became limited by serum growth factors which, when serum was fractionated by the low temperature ethanol procedure, appeared to precipitate with the alpha-globulins, although the distribution of activity varied from batch to batch of serum. Column chromatography (DEAE and concanavalin A-Sepharose) of serum resulted in much (20 to 45%) loss of growth factor activity during exhaustive dialysis or Sephadex G-25 desalting suggesting that the growth factor may be a diffusible molecule bound in serum to a large protein carrier.

Factors influencing the formation and stability of D-glucoside 3-dehydrogenase activity in cultures of Agrobacterium tumefaciens

D-glucoside 3-dehydrogenase specific activity in Agrobacterium tumefaciens was maximal towards the end of the exponential growth phase of batch cultures; over 90% of the activity disappeared within the next 15 h. Manganese ions, although essential for growth of the organism, strongly repressed D-glucoside 3-dehydrogenase synthesis in sucrose medium but had little effect when the carbon source was methyl alpha-D-glucoside. D-Glucoside 3-dehydrogenase activity increased linearly with increasing specific growth rate in chemostat cultures limited by carbon, nitrogen, phosphate or manganese when methyl alpha-D-glucoside was the carbon source. High enzyme activity was found with sucrose as carbon source only when the growth medium was manganese-limited. D-Glucoside 3-dehydrogenase activity disappeared from A. tumefaciens incubated in carbon- and nitrogen-free medium or in nitrogen-free medium containing succinate, but on continued incubation the activity returned and was then stable. The recovery of activity could be prevented by chloramphenicol or erythromycin. Bacteria containing the recovered dehydrogenase activity could not convert sucrose to 3-ketosucrose when oxygen acted as the terminal electron acceptor, but produced 3-ketosucrose at the normal rate in the presence of ferricyanide. D-Glucoside 3-dehydrogenase activity disappeared irreversibly from bacteria incubated in nitrogen-free medium containing sucrose. Loss of activity followed first order kinetics in bacteria taken from nitrogen-, phosphate- or manganese-limited chemostat steady states; an accelerating rate of decay occurred in cells grown under carbon-limitation. 8-Hydroxyquinoline, chloramphenicol, erythromycin, 2,4-dinitrophenol and manganese ions could reduce the rate of decay.

Growth dynamics of Agrobacterium tumefaciens in chemostat cultures limited by carbon source and mineral nutrients

Agrobacterium tumefaciens was grown in a chemostat in a chemically-defined medium which hs alpha-methyl D-glucoside, magnesium, manganese, phosphate or urea as the growth-limiting nutrient. Steady-state biomass concentrations were dependent on the specific growth rate of the organism when alpha-methyl D-glucoside, manganese or phosphate were growth-limiting nutrients. During magnesium-limited growth, large undamped oscillations in biomass concentration occurred. In all chemostat cultures a variant organism was selected which had lost the ability to grow in the medium supplied, bur survived on products of carbon metabolism derived from the wild-type.

The quantitative requirements of human diploid cells (strain MRC-5) for amino acids, vitamins and serum

The uptakes of all essential amino acids, vitamins (except riboflavin), glucose and serum during growth of human diploid cells (MRC-5) were determined. The amino acid uptakes varied considerably with the conditions of culture. The glucose requirement is several times greater than that for mouse LS or human HeLa cells. These analytical results were used to modify the medium so as to ensure that an excess of all defined medium constituents was present and pH was not limiting during study of the serum requirements. It was then found that maximum cell populations were directly proportional to the serum concentration. Hence the growth was limited by the supply of an unknown growth factor in serum. The serum growth factor was not replaced by a mixture of over 60 vitamins, co-enzymes, hormones and other organic and inorganic compounds considered to be possible growth factors, although this mixture did not lower the growth rate and somewhat (22%) increased the yield from the serum growth factor. The unit of serum growth factor is precisely defined in terms of the amount in a standard batch of calf serum. This standard contains 10 units/ml whereas the other batch of serum used contained only 5 units/ml.

Relationship between energy substrate utilization and specific growth rate in Aspergillus nidulans

The maintenance coefficient of glucose-limited Aspergillus nidulans chemostat cultures at 30 C was 0.018 g per g (dry weight) per hr for glucose and 0.55 mmoles per g (dry weight) per hr for oxygen. These values can only be approximate because melanin was produced by the mold at low growth rates and because it is unlikely that this polymer contributed to the maintenance energy requirement although it contributed to the dry weight. Biomass (defined here as dry weight minus melanin) was used to calculate a more meaningful maintenance coefficient for glucose (0.029 g of glucose per g of biomass per hr). At the highest growth rates examined, a nonlinear relationship between growth rate and glucose utilization rate was obtained, suggesting a qualitative change in the metabolic activities of the mold at high growth rates. The oxidative capacity of the mold was highest at the highest growth rates. This observation indicates that the increased substrate utilization rate observed at the higher growth rates is a reflection of enhanced enzyme synthesis. This hypothesis was verified by assaying the specific activities of several enzymes at different growth rates. However, in contrast to all the other enzymes assayed, the activities of reduced nicotinamide adenine dinucleotide phosphate: (acceptor) oxido-reductases were highest at the lowest growth rates.

The Glucose, Insulin and Glutamine Requirements of Suspension Cultures of HeLa Cells in a Difined Culture Medium

The serum supplement in a defined medium for the growth of HeLa cells could be replaced by protamine-zinc-insulin (0.2 u./ml). Insulin (0.4 u./ml) replaced the growth-stimulatory properties of protamine-zinc-insulin, whilst protamine sulphate (5 µg/ml) was found to be toxic to the cells. The addition of insulin to cultures depleted of insulin increased both cell growth rates and maximum cell populations. In the defined medium, HeLa cells could only utilize glutamate when a small amount of glutamine was included. Glucose, at a level of 2 mg/ml, was shown to limit maximum cell populations. The growth yield from glucose was 295 µg cell dry weight/mg glucose. When the medium glucose concentration was increased to 4 mg/ml, HeLa cell populations in excess of 16 x 105 cells (i.e. 640 µg dry weight)/ml were routinely achieved in the defined medium supplemented with insulin. Growth is then limited by the amino acid supply. Increasing the amino acid concentration of the medium by 50% raised the maximum cell population to 23.5x105 cells (i.e. 940 µg dry weight)/ml.

The Quantitative Glucose and Mineral Nutrient Requirements of Mouse LS (Suspension) Cells in Chemically Defined Medium

The influences of glucose, phosphate, magnesium and potassium concentration on growth rate and maximum population density were studied. From the data obtained the growth yields for glucose and phosphorus were found to be 2.4 x 105 cells (i.e. 0.76 mg dry weight)/mg glucose and 2.2 x 105 (i.e. 69 µg dry weight)/µg P. The growth response to magnesium and potassium was complex since there were threshold concentrations of these metals below which no growth occurred. The growth yield for potassium (2.4 x 105 cells (i.e. 75 µg dry weight)/µg K) was obtained by measuring potassium uptake during growth. Omission of calcium ions from the medium resulted in poor reproducibility of growth.

The Uptake of Vitamins by Mouse Fibroblast Cells (Strain LS) During Growth in a Chemically Defined Medium

The uptake of biotin, choline, folic acid, hypoxanthine, inositol, nicotinamide, pantothenic acid, pyridoxine, riboflavin, thiamine and vitamin B12 by mouse LS cells in suspension culture was determined by microbiological assay methods. Based on the extent of uptake during cell growth, vitamin growth yields (cells produced/unit mass of vitamin utilized) were estimated for all of the vitamins, except folic acid, thiamine and B12. The growth yields were lower during the early phases of culture. No uptakes of folic acid or B12 could be demonstrated. During the period of incubation about half of the thiamine was irretrievably lost through spontaneous decomposition.

Improvements in a Chemically Defined Medium for the Growth of Mouse Cells (Strain LS) in Suspension

In the medium used in previous work, both growth rate and maximum cell population density were reduced in protein-free medium. This was due to iron limitation. In a medium supplemented with iron, the average minimum population doubling time was reduced from 78 to 37 h and the average maximum cell population density increased from 1.6x106 to 3.3x106/ml.

In the improved medium described, sodium pyruvate, α-ketoglutaric acid, methylcellulose and polyvinylpyrrolidone are no longer required although methylcellulose prevents an initial fall in population which occurs in polymer-free medium. The present study indicates that amino acids now limit maximum cell population density. By increasing the concentration of the relevant amino acids we have obtained maximum cell populations in excess of 5.106 cells/ml without medium change.

Finally we describe a method for measuring the growth of the LS cell in the defined medium by an opacity method.

The Choline and Serum Protein Requirements of Mouse Fibroblast Cells (Strain LS) in Culture

The maximum cell population density of mouse fibroblast (strain LS) cells growing in static suspension culture was found to be directly proportional to the dialysed calf serum concentration. This was due to choline limitation and the fact that serum protein was a major source of choline. The growth yield (Y) was 3.2 x 105 cells/µg choline chloride.

Studies on the role of serum in the presence of excess choline showed the following. When protein was omitted from the medium, cell death occurred. Whole serum protein could be replaced by either (1) bovine serum albumin fraction V, or (2) crystalline bovine serum albumin + sodium pyruvate and α-ketoglutarate, or (3) polyvinylpyrrolidone + methylcellulose + pyruvate and α-ketoglutarate.

The population doubling time was 24 h in the presence of whole serum protein and increased considerably with the substitutes (1-3). The increase in maximum cell population density (without medium changes) exceeded 2.9 x 106 cells/ml with either whole serum protein or substitutes (1) and (2). With serum substitute (3) the maximum increase in population density was reduced to 1.6 x 106 cells/ml.