Comparison of the effects of carbon, nitrogen and iron limitation on the growth and on the RNA and DNA content ofmycobacterium smegmatis

Mycobacterium smegmatis was grown in shaken culture in carbon-, nitrogen- and iron-limited media, adjusted to decelerate at about the same time. The exponential phase was brief; the initiation of a more prolonged deceleration phase being probably due to the granular form of growth. Iron-limited cultures showed prolonged slow growth. In all three cultures the RNA/nitrogen ratio was high at the beginning of the period of maximal growth and declined thereafter. The DNA/nitrogen ratio also declined in the iron-limited cultures, but increased somewhat in the nitrogen-limited cultures and, after a brief decline, increased markedly in the carbon-limited cultures. In all cultures the soluble deoxyribonucleotide pool stayed within the range of 10–50 μmoles/g. of nitrogen, while the total soluble nucleotide pool fell from about 1000 to about 250 μmoles/g. of nitrogen as the growth rate declined.