82 CARBON NUTRITION 



Formic acid has been used as substrate in metabolic studies and 

 apparently supports at least limited growth (6, 15, 38, 76) but is 

 never a good source of carbon. Its low nutritional value, however, 

 does not exclude it or its derivates from an active role in metabolism. 



6. THE LIPIDS 



Perhaps because of the technical difficulty in the use of water-insolu- 

 ble substrates, the lipids have been little studied. However, it seems 

 clear that many fungi are able to grow on crude or purified natural 

 fats and oils (62, 89, 162a). Similar observations, incidental to meta- 

 bolic studies, indicate that some of but not all the higher fatty acids 

 support the growth of Mucor mucedo (197) and Penicillium glaucum 

 (212, 213). The quantitative data of Tausson (205) are reproduced in 

 Table 2; although the absence of controls somewhat reduces their sig- 



Table 2. The Utilization of Fats by Aspergillus flavus* 



Dry Weight, Utilization, 

 Experiment Carbon Source 



1 Cocoa butter 

 Coconut oil 



2 Oleic acid 

 Stearic acid 

 Palmitic acid 

 Tristearin 

 Tripalmitin 



* From Tausson (205), by permission of the Biochemische Zeitschrift. 



nificance, it is clear that both fats and fatty acids are utilized and 

 support growth in a medium containing no other source of carbon. 



It has been observed that cholesterol and other steroids support the 

 growth of Proactinomyces spp. (217, 218), and that some fungi make 

 visible growth with ergosterol as carbon source (177). Earlier work 

 on crude steroids suffers from the probability of contamination with 

 other carbon compounds. 



Numerous fungi and actinomycetes grow on crude or purified hydro- 

 carbons. The evidence, reviewed by ZoBell (246, 247) is largely ob- 

 servational only. Proactinomyces opacus grows on and oxidizes dode- 

 cane and tetradecane (231). Actinomycetes as a group appear to be 

 more active than fungi in attack on paraffins, other hydrocarbons, and 

 steroids (60, 98, 219). 



