66 FATTY ACID METABOLISM IN MICROORGANISMS 



tions of "C2" units, is converted into palmitoleic acid and 

 finally aWaccenic acid. 



Decanoate (upper right) may undergo the same types of 

 chain elongation as octanoate with formation of 3,4-dodecen- 

 oic acid via the hypothetical 3-hydroxydodecanoate. Chain 

 elongation of 3,4-dodecenoic acid by subsequent "Co" addi- 

 tions brings about formation of oleic acid via 7,8-hexadecen- 

 oic acid. Concurrently, both octanoate and decanoate may 

 undergo chain elongation with formation of palmitic and 

 stearic acids. This biosynthetic route to monounsaturated 

 fatty acids differs markedly from that present in yeast 

 M. phlei and mammalian liver which involves dehydrogena- 

 tion of palmitic or stearic acids via reactions requiring oxy- 

 gen and TPNH (4). 



3. METABOLISM OF MONOUNSATURATED FATTY 

 ACIDS IN BACTERIA 



Lactobacilli cannot synthesize saturated or unsaturated 

 fatty acids in absence of biotin, but cells grown on a supple- 

 ment of oleic or cf^-vaccenic acid contain large proportions 

 of saturated fatty acids, mainly palmitic acid. Since the 

 media employed are supplemented with Tween 40 (sorbitan 

 monopalmitate) the Tween may have provided the source 

 for the palmitic acid. As has been mentioned (Chapter 2, 

 section 3 and Chapter 3, section 1), the Tween is essential 

 for growth of many organisms on biotin-low media supple- 

 mented with unsaturated or cyclopropane fatty acids. 



Our own experiments (8) (Fig. 3.6) and those of our 

 former collaborator O'Leary (9) with L. arabinosus cultured 

 on ciVvaccinate-l-C^^ eliminate saturation of monounsatu- 

 rated fatty acids as a route to saturated fatty acids in this 



