62 FATTY ACID METABOLISM IN MICROORGANISMS 



be more complex than to serve merely as a source of satu- 

 rated fatty acids. Lactobacilli fail to grow on media low 

 in biotin which are supplemented with unsaturated fatty 

 acids and contain a saturated fatty acid in place of the 

 Tween. 



C?5-3,4-niethylenedecanoic acid, the cyclopropane analog 

 of aVS-decenoic acid fails to promote growth of the or- 

 ganisms. The synthetic precursor acetylenic acids of the 

 unsaturated acids, i.e., 3-decynoic, 5-dodecynoic, 7-tetrade- 

 cynoic and 11-octadecynoic acids also lack growth promoting 

 ability. 



2. STUDIES WITH LABELED COMPOUNDS 



That long-chain saturated fatty acids are incorporated 

 into the lipids of L. planarum and C. hutyricum is evident 

 from the results which are summarized in Table 3.1. Stearic 

 acid labeled with C^^ is incorporated into the bacterial 

 lipids, but the label is located almost exclusively in the 

 saturated acid fraction. Labeling of the unsaturated fatty 

 acids is insignificant. 



TABLE 3.1 

 Lack of Desaturation of Stearate in Anaerobic Bacteria 



C^^ stearate added 

 G^** incorporated 

 Total saturated acids 

 Total unsaturated acids 



Adapted from Bloch et al., Federation Proceedings, 20, 921 (1961). 



