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.