LACTOBACILLIC ACID 29 



Lactobacillus arabinosus and L. casei respond to unsaturated 

 as well as cyclopropane fatty acids. With L. casei, the 

 activity of the cyclopropane acids almost equals that of the 

 unsaturated acids. The position (9,10 or 11,12) and stereo- 

 chemistry {cis or trans) of the cyclopropane ring appears to 

 exert little effect on the microbiological activity. Lactobacil- 

 lus delbrueckii is more fastidious than L. arabinosus and 

 L. casei; it responds well to oleic, ce^-vaccenic, and elaidic 

 acids, but grows poorly on ^raw5-vaccenic acid. DL-cf5-9,10- 

 Methyleneoctadecanoic and lactobacillic acid are growth 

 promoting; DL-^rfln5-9,10-methyleneoctadecanoic acid exhib- 

 its a low order of activity and DL-^ran5-ll,12-methyleneocta- 

 decanoic acid is inactive. Lactobacillus acidophilus exhib- 

 its a marked preference for the cis isomers of the various 

 fatty acids. It is stimulated by ce.s-vaccenic, lactobacillic 

 and DL-cw-9,10-methyleneoctadecanoic acids, but fails to re- 

 spond to the corresponding trans isomers, regardless of 

 whether they are derived from unsaturated or cyclopropane 

 fatty acids. Shifting of the ring from the 9,10- to the 11,12- 

 position does not influence microbiological potency. The 

 observation that L. acidophilus grows in presence of lacto- 

 bacillic and DL-<:?5-9,10-methyleneoctadecanoic acid, but fails 

 to respond to the trans isomers, provides biological support 

 for the assigned cis configuration of lactobacillic acid. Clos- 

 tridium butyricum responds to oleic, czVvaccenic, linoleic, 

 and linolenic acids but is not stimulated significantly by the 

 other compounds. This result is unexpected, since the or- 

 ganisms contain both Cu and C19 cyclopropane fatty acids 

 (37). 



Based on this experimental evidence, it must be con- 

 cluded that certain long-chain cyclopropane fatty acids share 

 with long-chain unsaturated fatty acids the ability to pro- 



