Control of Bacterial Cell Growth and Composition 345 



0.2 0.4 



RNA/PROTEIN 



0.6 



Fig. 3. The relationship between growth rate and RNA 

 content of Aerobacter aerogenes, strain 5-P-14. The 

 growi:h rate constant, k (hours -^), is defined elsewhere 

 (Neidhardt and Magasanik, 19566), and the RNA content 

 is expressed as the RNA: protein ratio based on colori- 

 metric measurements. Each of the numbered points in the 

 figure represents the average of at least two experiments, 

 analysed in duplicate. The cells were grown (aerobically, 

 at 37°) in the various media for at least three generations 

 before any samples were taken. Except where indicated 

 otherwise, all of the media contained basal salts supple- 

 mented with excess amounts of guanine (50 ^g./ml.) and 

 arginine (100 [jtg./ml.). The major carbon and energy 

 sources, supplied at 0-2 per cent final concentration 

 were: (1) myo-'\nos\to\, with arginine supply limited by 

 the chemostat; (2) L-histidine; (3) glucose, with arginine 

 supply limited by the chemostat; (4) w?/o-inositol ; (5) 

 glucose, with the supply of arginine by the chemostat 

 greater than in (3) but still limiting ; (6) glycerol; (7) 

 L-histidine plus hydrolysed casein; (8) glucose; (9) 

 glycerol plus hydrolysed casein; (10) m^/o-inositol plus 

 hydrolysed casein. 



vary its content of protein-forming machinery. Bacteria 

 handle their resources with great economy : we have seen that 



