CULTURE MEDIA 21 



COMPARISON OF MEDIA 



Media differ only in constituents and amounts used. It is desirable to 

 be able to compare media in some uniform way. To do this, it is neces- 

 sary to know not only the amounts of the elements present, but also the 

 compounds in which these elements occur. A comparison of two syn- 

 thetic media is given in Table 3. 



From Table 3 it will be noted that these media contain the same essen- 

 tial elements. Copper, molybdenum, and gallium do not appear in the 

 composition of the glucose-asparagine medium, but it should not be con- 

 cluded that these elements were not present, since only c.p. chemicals 

 were used to prepare this medium. Stout and Arnon (1939) note that a 

 distinction must be made between ordinary chemical purity and biological 

 purity. This will be considered in detail in Chap. 5. The two features 

 which make these media quite distinct are the different sources of carbon 

 and nitrogen used and the addition of two vitamins to the glucose- 

 asparagine medium. The latter medium is suitable for the growth of 

 more species of fungi than is the sucrose-ammonium nitrate medium. 



SUMMARY 



Fungi secure food and energy from the substrates upon which they live 

 in nature. In order to culture fungi in the laboratory, it is necessary to 

 furnish in the medium those essential elements and compounds they 

 require for the synthesis of their cell constituents and for the operation of 

 their life processes. The synthetic abilities of fungi differ. Some fungi 

 are unable to s5Tithesize certain key compoimds that they require and 

 must obtain them from the medium upon which they grow. All the fungi 

 require much the same essential elements but differ widely in their ability 

 to utilize compounds in which these elements occur. There is no uni- 

 versal natural substrate or artificial medium upon which all fungi will 



grow. 



On the basis of composition there are three general types of media: 

 natural media, which are composed entirely of natural products; semi- 

 synthetic media, which are composed in part of natural substances; and 

 synthetic media, which are of kno^\^^ composition. Natural media are 

 most useful for routine work, while synthetic media and, to a limited 

 extent, semisynthetic media are used to investigate the nutritional 

 requirements of the fungi. Media differ only with respect to constituents 

 and concentrations. 



The compounds and the amounts used in preparing a medium must be 

 specified exactly. Media should be designated by naming the carbon 

 and nitrogen sources used, e.g., glucose-asparagine medium. The use 



