272 PHYSIOLOGY OF THE FUNGI 



crude lipide. A list of species of Penicillium and Aspergillus which syn- 

 thesize considerable fat is given in Table 48. 



Table 48. The Crude Fat Content op Dried Mycelium of Various Species op 

 PeniciUiuin and Aspergillus as Determined by Extraction with Ether 

 (Ward et al., Ind. Eng. Chem. 27, 1935. Published by permission of the American 

 Chemical Society.) 



Species Crude Fat, % 



Penicillium flavo-cinereum 28.5 



P. piscarum 26-28 



P. oxalicum 24.4 



P. roqueforti 22.9 



P. javanicum 22 . 2 



Aspergillus flavus 16.0 



Various theories of the mechanism of fat synthesis have been published 

 and are reviewed by Foster (1949) and Hesse (1949). Most of these 

 consider acetaldehyde or acetate to be the product of intermediary metab- 

 olism used in fat synthesis. This emphasizes the importance of pyruvic 

 acid in fungus metabolism. Various investigators have shown that 

 acetaldehyde may be converted into fat by yeasts. The glycerol required 

 for fat synthesis is thought to arise from the reduction and hydrolysis of 

 dihydroxyacetone phosphate or 3-phosphogly eerie aldehyde (scheme VI, 



Chap. 7). 



PRODUCTION OF VITAMINS 



Only a few species of fungi and bacteria produce vitamins in large 

 enough amounts to be of interest in industry. Biological synthesis must 

 compete with chemical synthesis on a cost basis. The recovery of vita- 

 mins as a by-product of commercial processes or the use of waste materials 

 as the basis of a cheap medium may make biological synthesis attractive. 



Riboflavin is produced so abundantly by Candida guilliermondi under 

 certain cultural conditions that it crystallizes in the medium (Burkholder, 

 1943). Among the factors found to influence the amount of riboflavin 

 synthesized, the sources of carbon and nitrogen and aeration are impor- 

 tant. Various investigators have found the concentration of iron in the 

 medium to have a profound influence on the amount of riboflavin syn- 

 thesized by various organisms. Iron concentrations in excess of 10 ^g 

 per liter decreased the amount of riboflavin synthesized by C. guillier- 

 mondi and C. fiareri (Tanner et al., 1945; Tanner and Van Lanen, 1947). 

 The optimum iron concentration for riboflavin synthesis by Clostridium, 

 acetobutylicum is said to be 1 mg. per liter. Hickey (1945) has suggested 

 the use of 2,2'-bipyridine to inactivate excessive concentrations of iron 

 in industrial fermentations. By maintaining the iron concentration 

 between 40 and 60 ng per liter, Levine et al. (1949) found the maximum 

 yields of riboflavin produced by C. guilliermondi and C. fiareri to be 175 

 and 567 ng per ml., respectively. Pilot-plant yields were somewhat less. 



