CHAPTER 2 

 CULTURE MEDIA 



Before discussing the nutrition of the fungi in detail, it will be helpful to 

 consider the basic problems involved. For many purposes a knowledge 

 of the nutrition of the fungi is necessary for culturing them in the labora- 

 tory or in industry. Like all living organisms the fungi must obtain from 

 their environment the materials needed for the synthesis of protoplasm 

 and other cellular constituents. Directly or indirectly, the fungi as well 

 as animals and most bacteria are dependent upon green plants for "food" 

 and energy. 



Not all natui'al substrates are equally suitable for all fungi. In nature, 

 the saprophytes are more widely distributed than the parasites, which are 

 usually restricted to the range of their hosts. Many of the substances 

 upon which the fungi grow in nature are chemically complex, and some, 

 such as cellulose, starch, and proteins are insoluble or are only colloidally 

 soluble. Before such compounds can be utilized, they must be changed 

 into low-molecular-weight compounds which are soluble in water. This 

 "digestion" is accomplished by means of enzymes which are excreted by 

 the fungi. This is analogous to digestion in animals, which is also an 

 enzymatic process. The complete utilization of a natural substrate is 

 frequently due to the combined action of a succession of microorganisms. 

 More than one organism may act at the same time, and often this simul- 

 taneous action is more effective than that of a single organism. 



One may ask. Do the fungi simply incorporate within their own proto- 

 plasm the suitable elements and compounds found in the medium, or do 

 they transform the compounds of the medium before building their own 

 structures? Apparently the fungi do both. The essential elements such 

 as potassium and magnesium are taken up as ions, although these ele- 

 ments may be in the state of chemical combination in the substrate and 

 also in the fungus cells. Certain organic compounds, such as the vita- 

 mins, are undoubtedly absorbed as such from the medium by vitamin- 

 deficient fungi; otherwise, these fungi would derive no benefit from them. 

 The same statement is true for other necessary compounds which the 

 various fungi are unable to synthesize. 



By far the greater part of the compounds utilized by the fungi are 

 modified or changed either before or after they are taken into the cells. 

 Outside the fungus cells, these changes are largely in the direction of 

 simplifying the molecular structure of compounds used. Within the 

 fungus cells some of the metabolite molecules are oxidized to carbon 



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