282 YEASTS AND YEAST-LIKE FUNGI 



Pichia and Zygopichia are distinguished by the fact that the former 

 forms spores after proHferation of diploid cells or is parthenogenetic 

 and the latter forms spores immediately after conjugation. The 

 cells of both genera are elongated and sausage-shaped. Each spore, 

 which is round, hemispherical, or angular, usually has a highly re- 

 fractile fat globule which is of diagnostic value. 



Hansenula and Zygohansenula. The latter is haplobiontic and the 

 former is diplobiontic or parthenogenetic. They are also film-form- 

 ing yeasts which form esters rather than alcohol, they are dominantly 

 oxidative and they utilize alcohol. The spores are angular or hemi- 

 spherical. These genera are found in the same habitats as Pichia 

 and Zygopichia. As more species are being found the morphological 

 differentiation of Pichia and Zygopichia from Hansenula and Zygo- 

 hansenula is breaking down. However, the utilization of oxygen 

 from nitrates resulting in the reduction of nitrates to nitrites by 

 Hansenula and Zygohansenula and the lack of this ability by the 

 other two genera points to a fundamental difference in metabolism 

 and, for the time being at least, it seems desirable to recognize all 

 four genera. If this criterion breaks down, species of Hansenula may 

 have to be transferred to Pichia, and Zygohansenula to Zygopichia. 



The best-known species Hansenula anomala, has characteristically 

 hat-shaped spores (Fig. 111). This species resembles Endomyco'psis 

 fibuliger, which also produces ethyl acetate, is film-forming and 

 oxidative, and possesses hat-shaped ascospores. Thus the relation- 

 ship to the higher Ascomycetes may be traced from the yeasts through 

 Hansenula and Endomycopsis, the latter of which, unlike the former, 

 has a well-developed true mycelium. Both Hansenula and Zygo- 

 hansenula are frequently referred to in the literature as Willia. Bed- 

 ford ^ has made a study of Hansenula and has recognized seven 

 species and three varieties. A determinative key is given. 



Debaryomyces. This genus is also a film- forming yeast and is 

 frequently found in the same habitat as the four preceding genera. 

 One or, rarely, two spores are found per ascus. These are rough 

 and warty. This roughness can best be seen if the cultures are in- 

 cubated at low temperatures as explained in Chapter HI. 



Saccharomycodes and Hanseniospora. These are apiculate yeasts, 

 that is, lemon-shaped with a small button-shaped production at each 

 end. In Saccharomycodes, the round spores conjugate during ger- 

 mination and in Hanseniospora, which is much more common, the 

 spores are formed by what Stclling-Dekker describes as partheno- 

 genesis. Hanseniospora is common on grapes, grows rapidly, and is 

 abundant during early fermentation. Since this yeast is sensitive to 



