38 FATTY ACID METABOLISM IN MICROORGANISMS 



tion of the latter organism consists of a mixture of cis-9,10- 

 hexadecenoic and czV7,8-hexadecenoic acids (12, 13). Sev- 

 eral strains of tubercle bacillus (4) and Mycobacterium phlei 

 contain oleic acid as the sole monounsaturated Cig com- 

 ponent. Polyunsaturated fatty acids do not occur in these 

 various microorganisms (14). 



3. FATTY ACID INTERCONVERSIONS IN 

 LACTOBACILLI 



The first clue pertaining to a close metabolic relation 

 between c?Vvaccenic and lactobacillic acids came from the 

 results (15) recorded on Table 2.3 which illustrate the effect 

 of variations in the growth medium on the fatty acid spec- 

 trum of L. delbrueckii. Since this organism requires Tween 

 40 (sorbitan monopalmitate) for maximal growth in pres- 

 ence of unsaturated fatty acids (16), information on the effect 

 of Tween 40 on the fatty acid spectrum is important. Com- 

 parison of the biotin cells (culture I) with the biotin plus 

 Tween 40 cells (culture II) shows the total fatty acid con- 

 tent of the latter to be almost twice that of the former. 

 Inspection of the fatty acid spectrum reveals a markedly 

 higher palmitic acid content of the Tween cells, but an 

 increase in the (Ci^ plus C19) and in the Qg fraction is also 

 observed. The "dihydroxy" fraction is lower than that of 

 the controls. Adsorption to the cell surface of palmitic 

 acid, derived from the Tween, may explain the high pal- 

 mitic acid content of the culture II cells, but the increase 

 in other fatty acids is hardly explicable along these lines. 

 It appears likely that, in addition to providing the organ- 

 isms with a source of palmitic acid, the Tween stimulates 

 fatty acid biosynthesis. 



