ADAPTATION TO PANTOTHENATE DEFICIENCY 



22-10 



independent strain is crossed by a dependent strain, the segrega- 

 tion obtained is always 2 dependent and 2 independent spores in 

 each four spored ascus. Ability to grow rapidly without pantothenate 

 is determined, in the pedigree, by the segregation of a single gene. 

 Clone 2154 is further characterized by being a non-fermenter of 

 both maltose and melibiose, and of mating type "a**. 



Fig. 22-3 Growth of cultures Nos. 20, 21, 22, and 23 (haplo- 

 phase segregants from S. carlsbergensis by S. cerevisiae hybrid) on 

 Burkholder' s medium containing different concentrations of panto- 

 thenate . 



The experiment to determine the effect of concentration of pan- 

 tothenate on adaptation was repeated with culture 2154. Figure 22-4 

 is the series of curves obtained by plotting amount of growth (in 

 colorimeter readings) against time in hours. From 200 > per liter 

 down to 2> per liter, both the rate of growth and the total amoxmt 

 of growth decreases as the amount of pantothenate decreases. This 

 is what would be expected if the organism requires pantothenate for 

 growth but is unable to synthesize it, at least in sufficient amount. 

 However, as the concentration reaches this critical point (27 per 

 liter) or drops below it, there is a long lag after which the culture 

 adapts and attains a rate and total amount of growth greater than 

 those at the intermediate concentrations. 



The adaptation is a permanent heritable change for the increased 

 rate of growth which occurs in the lowest concentrations is main- 



