Rate of ribosome production in Bacillus licheniformis

The ribosome content of exponential-phase cells of Bacillus licheniformis was measured at three different growth rates. The average number of ribosomes per cell was about 92,000, 34,400, or 12,500 70S equivalents in balanced cultures growing at 37 C with generation times of 35, 60, and 120 min, respectively. Since the ribosomal particles were shown to be metabolically stable in exponentially growing cells, these figures implicate large differences in the quantity of ribosomes synthesized per unit of time in an individual cell grown under the various conditions. Nevertheless, the time required for the biosynthesis of a single 50S subunit was constant (about 10 min) and independent of the specific growth rate of the cell (within the limits studied). These results show that ribosome production is not regulated by control of the rate of assemblage of individual ribosomes, but rather by control of the number of the ribosomes in manufacture at a time.