26-13 THE YEAST CELL 



(2) starved without sugar, (3) starved and fed glucose, (4) starved 

 and fed galactose, (5) starved and fed melibiose, and (6) starved 

 and fed maltose were then tested for their ability to ferment galac- 

 tose. (Culture 1208 originally required 4 to 5 days to ferment 

 galactose). Six of the 30 cultures fermented galactose in 4-5 days. 

 All others were faster, usually from 1-2 days except one starved 

 and fed melibiose, which failed to ferment, and a second also fed 

 melibiose, which was contaminated. 



Experiment V. Table 26-6 shows the results of an experiment 

 in which cultures dissimilated in M/SO KH0PO4 on the shaker for 

 20 days (1) in phosphate buffer and (2) in pnosphate buffer with glu- 

 cose. In all but one case, 5 isolated colonies from each haplophase 

 were tested. Each separate colonial isolate is indicated by a small 

 letter, 1208-a, etc. The numbers indicate the days before fermenta- 

 tion occurred. One isolate of 1211 in phosphate buffer failed to fer- 

 ment maltose and one of 1210 in phosphate buffer with glucose fail- 

 ed to ferment maltose; all others performed as well as the originals 

 except three which were slow in maltose. 



Experiment VI. The possibility that selecting colonies from a 

 natural medium might have restored fermentation vigor was inves- 

 tigated by selecting colonies from plates of Hutner's synthetic med- 

 ium and testing on the 4 sugars. Table 26-7 shows one failure on 

 galactose and one on maltose, but most others have their usual 

 speed of fermentation. 



Experiment VII. Finally, the dissimilation and starvation tech- 

 nique was tested by isolating individual colonies from the original 

 stock cultures on our standard peptone -yeast extract agar and 

 Hutner's synthetic medium agar (Table 26-8). Three isolates from 

 Hutner's medium were unable to ferment galactose and one was very 

 slow (29 days). These results indicate that dissimilation and star- 

 vation give no result that cannot be obtained by direct isolation on 

 a deficient medium. 



Experiment VIII. Haplophase 557 (Table 26-5) is a parent which 

 produced many progeny vigorously capable of fermenting both meli- 

 biose and maltose when mated to a nonfermenter of these sugars. 

 It is genotypically designated g ME MA. In Experiment I, a culture 

 of 557 was obtained which fermented maltose only after 12 days. 

 Thirteen colonies were obtained from this culture. Cultures from 

 each of these 13 colonies were transferred daily for 11 times through 

 5cc each of 4 per cent glucose broth. The cultures were plated on 

 peptone-yeast extract agar. Single colonies were suspended in 

 M/15 phosphate buffer and 2 drops of this suspension used to inocu- 

 late small fermentation tubes of galactose, maltose, melibiose, and 

 sucrose. The cultures were observed from 11/^1 to 12/26 for fer- 

 mentative ability, by which time the fermentation tubes had dried 

 up. 



