ADAPTATION TO PANTOTHENATE DEFICIENCY 22-36 



added, it appears that all the sugar had been exhausted by the inef- 

 ficiently growing unadapted cells. However, since addition of sugar 

 made possible only a small increase in growth, it would appear that 

 there were other factors in addition to exhaustion of sugar which 

 prevented the adapted cells from attaining maximum growth. Fur- 

 ther work will be required to determine whether this inhibition be 

 due to exhaustion of other nutrients in addition to sugar or to ac- 

 cumulation of harmful by-products or both. 



The reason the adapted culture does not reach the same high 

 rate of growth as the unadapted in the presence of opt inal concen- 

 trations of pantothenate may be due to a slight decrease in efficiency 

 of growth caused by the extra "load" of synthesizing pantothenate. 

 Other pantothenate synthesizing cultures bearing the A gene grow as 

 rapidly as unadapted 2154 in the presence of a large amount of pan- 

 tothenate so we cannot assume that ability to synthesize pantothenate 

 in general depresses growth rate. In this particular case since we 

 know the adapted strain synthesizes the vitamin by an alternate 

 route it may be that this diverts an intermediate in the synthesis 

 of some other growth factor so that the rate of growth is depressed. 



This inhibition of growth of mixed cultures in intermediate a- 

 mounts of the essential growth factor appears to be the same phe- 

 nomenon as that studied by Ryan and Schneider (1948) of the inter- 

 action between histidineless and histidine independent cells of 



apparently have not reached a population large enough to limit 

 seriously the secondary growth of the adapted mutant. The growth 

 in the long primary phase may be due to synthesis of pantothenate 

 by the recessive genes present in the unadapted cells. Ihere is 

 apparently little or no lag in the growth of unadapted cells in 

 concentrations of pantothenate fron. 200 to 5 micrograms per liter. 

 However, when 2 micrograms of pantothenate are present, a short 

 lag occurs during which the recessive (unadapted) organism is 

 adapting to growth in the mediuh and possibly to the slow syn- 

 thesis of pantothenate. When 1 microgram is present a slightly 

 longer lag occurs, indicating that the extra microgram of panto- 

 thenate is of considerable assistance in speeding up the growth 

 of the unadapted cells. Correspondingly, in the absence of added 

 pantothenate an even longer lag occurs than in the medium contain- 

 ing 1 microgram. The upward swing of these curves, after the pri - 

 mary adaptation, is due to the mutation from the unadapted to the 

 adapted form. It depends on the production of a population suf- 

 ficiently large to assure the presence of one or more mutants. 

 Small variations in the amounts of pantothenate below the critical 

 level of 2 micrograms are directly reflected in the time at which 

 the primary adaptations occur. 



