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

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.