NUTRITIONAL REQUIREMENTS OF MOLDS 217 



NUTRITIONAL REQUIREMENTS OF MOLDS 



Adequate supplies of elements such as carbon, nitrogen, hydrogen, 

 oxygen, phosphorus, sulphur, and magnesium must be furnished the 

 molds. 



The sugars, sucrose, glucose, or fructose, serve as excellent sources 

 of carbon for most fungi. Other sugars including pentoses, alcohols, 

 organic acids, oils, higher paraffins, and polysaccharides have also 

 proved capable of satisfying, at least partially, the carbon require- 

 ments of certain molds. Tamiya,*'^ who has carried out one of the 

 more elaborate studies on the relation between chemical structure 

 and assimilability, has made the interesting observation that some 

 compounds can serve satisfactorily for respiration but not for growth. 

 He further noted that no constant relation exists between respiration 

 and growth since the former was found to vary with the source of 

 carbon. Steinberg **" has noted that practically all tests of assimil- 

 ability of a carbon source are based on experiments with pure com- 

 pounds. Since fungi under normal conditions grow on mixtures of 

 carbon compounds, he has suggested that the results of tests with 

 single carbon sources cannot serve as final tests of assimilability. 



In general, the molds are capable of utilizing a large number of 

 nitrogen compounds. Robbins ^^ has suggested that fungi fall into 

 four groups when classified on the basis of their nitrogen require- 

 ments. The groups may be referred to as the nitrogen-fixing, the 

 nitrate, the ammonium, or the organic nitrogen compound users. 

 The first group, according to Robbins, is capable of utilizing 

 nitrate, ammonium, or organic nitrogen in addition to being able to 

 use atmospheric nitrogen. Those organisms in the second group, in- 

 capable of using gaseous nitrogen but able to use nitrate nitrogen, 

 can grow also with ammonium or organic nitrogen sources. The 

 organisms of the third group are capable of developing only in the 

 presence of ammonium or organic nitrogen compounds. The last 

 group consists of those organisms which can satisfy their nitrogen 

 requirements only with organic nitrogen sources. However, it should 

 be noted and emphasized here in connection with the first group 

 of molds that the belief in the general ability of the fungi to fix 

 gaseous nitrogen is no longer held. Therefore, there would be very 

 few, if any, molds which would be placed in the first group. It should 

 also be pointed out that the nitrogen requirements of an organism 

 are not fixed but vary with the source of carbon. Robbins' scheme 



