CHAPTER 9 

 VITAMINS AND GROWTH FACTORS 



It is kno^\^l that, for normal growth and development, animals and 

 man require in their diet minute amounts of certain organic compounds, 

 in addition to those which yield energy or are used for structural purposes. 

 Similarly, certain fungi must obtain from the substrate some of the same 

 substances for growth, reproduction, and other vital functions. Other 

 fungi are able to synthesize these compounds, which are called groivth 

 factors, or vitamins. Both terms have often been applied to the same 

 compounds, although the terms are not always synonymous. Originally, 

 the term vitamin was applied to the accessory factors in animal nutrition, 

 and some workers would restrict its use to animals and man. The term 

 growth factor has a somewhat broader connotation than vitamin. It 

 includes the components and derivatives of some vitamins, as well as 

 other compounds which cannot be classified otherwise at present. The 

 chemical names of the vitamins also may be used. 



GENERAL CONSIDERATIONS 



A number of vitamins, such as thiamine and biotin, have been shown 

 to perform definite functions in fungi as well as in animals, and there is 

 no reason to assume that the fundamental functions in the two groups 

 of organisms are essentially different. The characteristic features of a 

 growth factor (vitamin) include the following: (1) its organic nature; (2) 

 its activity in minute quantities; (3) its catalytic action; (4) the specificity 

 of its action. It is known that some vitamins are components of enzyme 

 systems, and it may be assumed that all act in this way. 



In the fungi the relative effects of the presence of vitamins in the 

 medium usually are measured by the resultant vegetative growth, 

 although vitamins are known to affect reproduction and other processes. 

 Needless to say, studies of vitamin deficiencies must be carried out under 

 carefully controlled conditions, using clean glassware, purified chemicals, 

 and precaution against contamination. Despite all precautions possible, 

 variable results often occur, and tests may need to be repeated several 

 times before the vitamin deficiencies of some fungi can be definitely 

 determined. 



SYNTHESIS OF VITAMINS BY FUNGI 



Many fungi are able to grow and develop normally on a substrate con- 

 taining no vitamins. For example, Aspergilhis niger grows well on a 



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