58 FATTY ACID METABOLISM IN MICROORGANISMS 



with the failure of saturated fatty acids to exert the typical 

 sparing action of unsaturated fatty acids on the biotin re- 

 quirements of various lactic acid organisms (Chapter 1, sec- 

 tion 6) eliminated direct desaturation of long-chain satu- 

 rated fatty acids as the pathway to unsaturated fatty acids. 

 As it appeared more likely that the organisms introduce the 

 unsaturation into a smaller molecule, which would then 

 undergo elongation of its carbon chain through successive 

 2-carbon additions, we synthesized three unsaturated fatty 

 acids of the general structure shown on Fig. 3.1 (where n 

 represents 1, 3, and 5) and tested their ability to support 

 growth of L. arahinosus, L. casei, and L. delbrueckii in 

 presence of suboptimal amounts of biotin. Starting with 

 ciVvaccenic acid (n = 9) and including palmitoleic acid 

 (n = 7) a homologous series of five unsaturated acids differ- 



H3C — (CH2)5 (CH2)„— COOH 



C C[ 



U H 



Fig. 3.1. Chemical structure of homologous series of unsaturated 

 fatty acids. 



