Ribonucleic acid composition of bacteria as a function of growth rate

Abstract

Ribonucleic acids extracted from Escherichia coli, Salmonella typhimurium and Aerobacter aerogenes grown at different growth rates in media containing various carbon and nitrogen sources were fractionated by adsorption on methylated serum albumin columns and elution with salt concentration gradients. In all three species, the fraction of total RNA eluted at low salt concentrations was found to decrease at increasing growth rates. In E. coli and S. typhimurium, this fraction tends towards a minimum value, which is practically reached at a growth rate of 0·4 to 0·5 at 30°C, and does not significantly change at higher growth rates. In A. aerogenes, the decrease is more continuous and apparently linear over the range of growth rates tested in the present experiments. Since most of the RNA eluted at low salt concentrations is transfer RNA, whereas RNA eluted at higher salt concentrations corresponds to ribosomal RNA, it may be concluded that the syntheses of transfer and ribosomal RNA's are regulated independently at low growth rates in E. coli and S. typhimurium and probably at all growth rates in A. aerogenes. Various hypotheses to account for this differential control are discussed. The efficiency of ribosomes in protein synthesis in E. coli has been evaluated at growth rates higher than 0·4 and found to decrease with decreasing growth rate.