28 FATTY ACID METABOLISM IN MICROORGANISMS 



20% of the fatty acids, the organism also contains lacto- 

 bacillic acid. Clostridium hutyricum, according to Bloch 

 et al. (37), contains a family of cyclopropane fatty acids 

 with 13, 15, 17, and 19 carbon atoms, respectively. Evi- 

 dence for the presence in microorganisms of position iso- 

 meric methyleneoctadecanoic acids is presented in Chapter 

 3, section 3. 



6. MICROBIOLOGICAL ACTIVITY OF 

 CYCLOPROPANE FATTY ACIDS 



The marked biotin-sparing activity of oleic acid in the 

 nutrition of a variety of microorganisms, originally described 

 by Williams and Fieger (1), was confirmed and extended 

 by a number of investigators (2-7). These studies have 

 shown that long-chain mono- and polyunsaturated fatty 

 acids of both the cis and trans series have this biological 

 property. Saturated fatty acids are inactive but may exert 

 a synergistic effect when supplied to the organisms in con- 

 junction with unsaturated acids (5). The cis isomers of a 

 number of position and stereoisomeric monoethenoid 

 octadecanoic acids exhibit practically the same biotin-spar- 

 ing activity for L. arahinosus regardless of the position of 

 the double bond. With exception of elaidic acid, which 

 possesses a high degree of biotin-sparing potency, the trans 

 isomers are less active than the corresponding cis forms, and 

 the activity decreases in a stepwise manner, as the double 

 bond is shifted from the center of the chain toward either 

 the methyl or the carboxyl end (38). We find (39) that 

 certain cyclopropane fatty acids share with the unsaturated 

 fatty acids the ability to bring about microbial growth in 

 presence of suboptimal quantities of biotin (Table 1.3). 



