Chapter IX 



AQUATIC YEASTS AND MOLDS 



Technically speaking, yeasts and molds as well as bacteria are Fungi. 

 Fungi may be defined as achlorophyllous plants constituting a primary 

 division of the phylum Thallophyta, co-ordinate with the Algae which 

 contain chlorophyll. The division Fungi comprises the classes Myxo- 

 mycetes (slime molds) , Eumycetes (true fungi), and Schizomycetes (fission 

 fungi or bacteria). The class Eumycetes consists of the sub-classes 

 Phycomycetes, Ascomycetes, Fungi Imperfecti, and Basidiomycetes. 

 Though primarily terrestrial, all sub-classes of Eumycetes except the 

 Basidiomycetes have a number of aquatic representatives. No species of 

 Basidiomycetes have been found living normally in bodies of water. 

 Several hundred representatives of the Phycomycetes and smaller num- 

 bers of Ascomycetes and Fungi Imperfecti live in aquatic environments. 



Organisms which in popular parlance are known as molds or mold fungi 

 embrace certain orders of Phycomycetes, Fungi Imperfecti, and Ascomy- 

 cetes. The latter also includes, besides other orders, the Saccharomy- 

 cetales or yeasts. The true yeasts multiply by budding or by the forma- 

 tion of ascospores, hence the sub-class name, Ascomycetes, to which they 

 belong. The so-called wild yeasts or torulae belong to a family of Fungi 

 Imperfecti, namely the Dematiaceae. Torulae, or wild yeasts, differ from 

 the true yeasts in that they do not form spores. The asporogenous 

 Mycoderma are also called wild yeasts. 



Occurrence of yeasts in the sea : — Yeasts are widely and commonly 

 distributed in nature. Though probably not as well adapted, as a class, 

 as bacteria to growing throughout a wide range of environmental condi- 

 tions, there are yeasts which are capable of tolerating nearly any ex- 

 tremes of osmotic pressure, hydrostatic pressure, temperature, ^H, or 

 oxygen tension found in the sea. Yeasts may be cultivated by the same 

 methods as are used for bacteria, and they are more readily enumerated 

 by direct microscopic counts than bacteria because, on the average, yeasts 

 are larger than bacteria and have a more distinctive morphology. 



In spite of the fact that, for the most part, special nutrient media rich 

 in carbohydrates or other utilizable organic matter have not been em- 

 ployed, many bacteriologists report finding yeasts in the sea. Colonies 

 of yeasts often appear along with bacteria on nutrient media designed 

 primarily to detect bacteria. Most of the reports fail to describe the 

 yeasts, so it is not known whether the organisms were true yeasts, torulae, 

 or other yeast-like organisms. Fischer and Brebeck (1894) reported 

 the presence of many Torula and Mycoderma and a few true yeasts in sea 

 water. They found Blastoderma salmonicolor in a sample of sea water 

 taken near the Azores Islands. It is problematical whether certain of 

 these organisms are indigenous to the sea because they occur so commonly 

 in the air. 



From the North Sea, Nadson and Burgwitz (1931) isolated 22 vari- 

 eties of yeast-like organisms including 15 varieties of white Torula, 7 of 



