SYMBIOSIS OF YEASTS 125 



proportion, two yeasts of the Pastorianus type; one A, was rather in- 

 active, the other B seemed to take part in the secondary fermentation. 

 But it is necessary to say that such associations in yeasts x are rare. 

 In most of the breweries where mixtures of yeasts are employed, it 

 is exceptional that an equilibrium is maintained between them. One 

 almost always predominates over the others. 



Certain fermentations in distilleries produced by mixtures of 

 fungi also seem to be cases of symbiosis. The fungi transform the 

 starch into maltose which the yeasts ferment. A large number of fer- 

 mented beverages used in different countries, resulting from the fer- 

 mentation of starch, seem to be due to such symbiotic associations of 

 yeasts and fungi. For example, Sake, an alcoholic, drink prepared 

 by the fermentation of rice, and used in Japan, is an example. This 

 beverage is obtained by the action of different organisms, among which 

 is Aspergillus oryzae and many yeasts and molds. The starch of the 

 rice is changed into maltose by Aspergillus oryzae and this sugar fer- 

 mented by the molds and yeasts. Arrack, obtained by the fermentation 

 of molasses and rice flour, is produced by an agent made up of bac- 

 teria, molds (Chlamydomucor oryzae, Rhyzopus oryzae) and two yeasts. 

 The fermentation in bread seems to result by the symbiotic action of 

 a yeast and bacteria. 



Another example of the same order has been mentioned by Lutz. 1 

 According to this author, tiby, an alcoholic drink of the Mexicans, 

 is produced by the action of a yeast, Pichia Radaisia, and a bac- 

 terium B. mexicanus, which live in symbiotic association. The yeast 

 living in contact with air is not able to induce fermentation. Asso- 

 ciated with the bacillus it brings about the alcoholic fermentation. The 

 bacterium plays its only role in keeping the concentration of oxygen 

 down. Lutz has been able to bring about an experimental symbiosis 

 with P. Radaisia and B. subtilis. 



Another classic example of symbiosis has been observed by Freu- 

 denreich 2 in kefir, the fermented milk. He has isolated 4 micro- 

 organisms: 1, the kefir yeast; 2, Streptococcus a which coagulates 

 the milk; 3, Streptococcus b which possesses probably a lactase; and 

 4, Dispora caucasica or Bacillus caucasicus whose role is not known. 

 According to Freudenreich, the yeast does not possess a lactase and is 

 thus unable to ferment lactose. This is accomplished by Streptococ- 

 cus b. This is, then, a symbiotic association. Jorgensen has observed 

 another yeast in kefir, S. fragilis, which possesses a lactase and is thus 



1 Lutz, L. Association symbiotique du Sacch. Radaisii. Bull, de la soc. myc. 

 de France, 1906. 



2 Freudenreich, E. Bakteriologische Untersuchungen iiber den Kefir. Cent. 

 Bakt. 3, 1897. 



