NUTRITION OF MICRO-ORGANISMS 



7-5 mg. per kg. for cats. The toxicity of leucopterine was of the 

 same order. 



References to Section 14 



1. B. K. Harned, R. W. Cunningham, H. D. Smith and M. C. Clark, 



Ann. N.Y. Acad. Sci., 1946, 48, 289. 



2. A. Taylor and N. Carmichael, Proc. Soc. Exp. Biol. Med., 1949, 71, 



544- 



3. H. Horlein, Arch. Exp. Path. Pharmakol., 1941, 198, 258. 



15. FOLIC ACID IN THE NUTRITION OF MICRO- 

 ORGANISMS 



Essential Growth Factors 



It has already been stated (page 457) that folic acid and the L. casei 

 factor were originally recognised by virtue of their ability to stimulate 

 the growth of L. helveticus (L. casei e) and 5. faecalis R, and that (page 

 459) vitamin Be, now known to be identical with the liver L. casei 

 factor, pteroylglutamic acid, although originally recognised as an 

 anti-anaemia factor for the chick, also stimulated the growth of these 

 two bacteria. The fermentation L. casei factor, pteroyltriglutamic 

 acid, however, is a growth factor for L. helveticus. but not for 5. 

 faecalis R, whilst vitamin Be conjugate, pteroylheptaglutamic acid, is 

 not a growth factor for either, but has to be converted into the mono- 

 glutamate by the action of vitamin Be conjugase before becoming, 

 effective (page 479). Pteroic acid and the SLR factor (rhizopterine), 

 on the other hand, are growth factors for S. faecalis R, but not for 

 L. helveticus. Finally, it is relevant to note that _^-aminobenzoic acid 

 is a growth factor in its own right, although its r61e in the nutrition 

 of micro-organisms is to some extent bound up with that of folic acid 

 (see page 563). 



Folic acid is also a growth factor for Clostridium tetani ^ and for 

 the ciliate, Tetrahymena geleii.^ The latter is unique among micro- 

 organisms in that its growth is stimulated by folic acid conjugate,^^ 

 which is twice as active as an equivalent weight of pteroylglutamic 

 acid. 



Synthesis of Folic Acid 



Most organisms, however, appear to be capable of synthesising 

 folic acid, although some will only do so if provided with a particular 

 part of the molecule. For example, Aerobacter aerogenes was found ^ 

 to synthesise folic acid, and the amount produced was materially 

 increased when xanthopterine was added to the culture medium. It 



509 



