Chapter 16 

 ADAPTATION IN A YEAST UNABLE TO UTILIZE GLUCOSE 



Monod (1942) analyzed the mechanism of adaptation of micro- 

 organisms to media containing mixtures of carbohydrates and de- 

 scribed the phenomenon of "D laux ie." 



Diauxic growth occurs when an organism adapts to two different 

 carbohydrates in sequence using first only one and after that has 

 been consumed using only the other. 



The substances for which the cell contains "constitutive" en- 

 zymes are used first and those for which it must produce "adap- 

 tive" enzymes are used secondly. Diauxie is not demonstrable for 

 every mixture of carbohydrates of the above combination but was 

 frequently demonstrated. He considers the difference between 

 "constitutive" and "adaptive" enzymes quantitative rather than 

 qualitative. 



Spiegelman and Dunn (1947) confirmed the interaction of en- 

 zymes attacking carbohydrates in yeasts and showed that adapta- 

 tion to galactose reduced the amount of the constitutive enzyme, 

 glucozymase. 



Glucozymase is one of the "constitutive" enzymes of the yeast 

 cell. However, if its production is under genetical control, it should 

 be possible to obtain mutants lacking one or more of the essential 

 enzymes. Skoog and Lindegren (1947) derived a culture incapable 

 of fermenting glucose from a hybrid between S. microellipsoideus 

 and S. cerevisiae. This culture was isolated in synthetic medium 

 containing lactate as a carbon source. The culture was stable for 

 nonfermentation of glucose as long as it was maintained with fre- 

 quent transfer on lactate medium but reverted to glucose fermenta- 

 tion if left in glucose for about 10 days or even if left in lactate for 

 a long time. It reverted immediately in peptone. This is apparently 

 a typical depletion mutation which can undergo repair in vegetative 

 reproduction. 



The culture grew in lactate alone without any evidence of a lag 

 period. That is, there was no adaptive period; the enzyme con- 

 trolling the use of lactate was "constitutive." In glucose alone a 

 long lag period of from 8-10 days was required. In mixtures of 

 lactate and glucose an irregular diauxic growth curve was produced. 

 But the presence of glucose inhibited the cell in its ability to utilize 

 lactate, for in mixtures of lactate and glucose a lag period always 

 intervened before growth began. 



16-1 



