Modulation of Chemical Composition and Other Parameters of the Cell by Growth Rate

Products, requirements and efficiency of biosynthesis: a quantitative approach

The amount of ATP required for the formation of microbial cells growing under various conditions was calculated. It was assumed that the chemical composition of the cell was the same under all these conditions. The analysis of the chemical composition of microbial cells of Morowitz (1968) was taken as a base. It was assumed that 4 moles of ATP are required for the incorporation of one mole of amino acid into protein. The amount of ATP required on account of the instability and frequent regeneration of messenger RNA was calculated from data in the literature pertaining to the relative rates of synthesis of the various classes of RNA molecules in the cell. An estimate is given of the amount of ATP required for transport processes. For this purpose it was assumed that 0.5 mole of ATP is necessary for the uptake of 1 g-ion of potassium or ammonium, and 1 mole of ATP for the uptake of 1 mole of phosphate, amino acid, acetate, malate etc. The results of the calculations show that from preformed monomers (glucose, amino acids and nucleic acid bases) 31.9 g cells can be formed per g-mole of ATP when acetyl-CoA is formed from glucose. When acetyl-CoA cannot be formed from glucose and must be formed from acetate, Y
 ATP
 MAX
 is only 26.4. For growth with glucose and inorganic salts a Y
 ATP
 MAX
 value of 28.8 was found. Addition of amino acids was without effect on Y
 ATP
 MAX
 but addition of nucleic acid bases increased the Y
 ATP
 MAX
 value to that for cells growing with preformed monomers. Under these conditions 15–20% of the total ATP required for cell formation is used for transport processes. Much lower Y
 ATP
 MAX
 values are found for growth with malate, lactate or acetate and inorganic salts. During growth on these substrates a greater part of the ATP required for cell formation is used for transport processes. The calculated figures are very close to the experimental values found. The interrelations between Y
 ATP
 MAX
 and YATP, the specific growth rate (μ), the maintenance coefficient (me) and the P/O rate are given. From a review of the literature evidence is presented that these parameters may vary under different growth conditions. It is concluded that in previous studies on the relation between ATP production and formation of cell material these effects have unjustly been neglected.

A theoretical study on the amount of ATP required for synthesis of microbial cell material

This review begins by briefly presenting the history of research on the chemical composition and other parameters of cells of E. coli and S. enterica at different exponential growth rates. Studies have allowed us to determine the in vivo strength of promoters and have allowed us to distinguish between factor-dependent transcriptional control of the promoter and changes in promoter activity due to changes in the concentration of free functional RNA polymerase associated with different growth conditions. The total, or bulk, amounts of RNA and protein are linked to the growth rate, because most bacterial RNA is ribosomal RNA (rRNA). Since ribosomes are required for protein synthesis, their number and their rate of function determine the rate of protein synthesis and cytoplasmic mass accumulation. Many mRNAs made in the presence of amino acids have strong ribosome binding sites whose presence reduces the expression of all other active genes. This implies that there can be profound differences in the spectrum of gene activities in cultures grown in different media that produce the same growth rate. Five classes of growth-related parameters that are generally useful in describing or establishing the macromolecular composition of bacterial cultures are described in detail in this review. A number of equations have been reported that describe the macromolecular composition of an average cell in an exponential culture as a function of the culture doubling time and five additional parameters: the C- and D-periods, protein per origin (PO), ribosome activity, and peptide chain elongation rate.

Modulation of Chemical Composition and Other Parameters of the Cell at Different Exponential Growth Rates.

Utilization of energy for growth and maintenance in continuous and batch cultures of microorganisms: A reevaluation of the method for the determination of ATP production by measuring molar growth yields

Thomas E. Norris

Papers

Effect of growth rate on the relative rates of synthesis of messenger, ribosomal and transfer RNA in Escherichia coli.