378 EIBOFLAVIN 



firmed," and the effect of several variations in the riboflavin structure on 

 the bacterial response was determined.^ The response proved very specific, 

 and on these grounds a microbiological assay for the vitamin was developed 

 and proposed.^ Both growth and acid production of lactic acid bacteria are 

 proportional to riboflavin in the suboptimal range of concentrations.^' ^ 

 Riboflavin is required as a growth factor by fewer microorganisms than 

 are most of the other vitamins;^- ^ besides the lactic acid bacteria, however, 

 many of the hemolytic streptococci, some propionic acid bacteria, some 

 Clostridia, and some luminescent bacteria require it. Few if any naturally 

 occurring yeasts or other fungi have been found that require riboflavin;^ 

 mutants of Neurospora crassa that require it have, however, been obtained ,'' 

 and all organisms so far examined that do not require preformed supplies 

 of this vitamin synthesize it.^' ^ Indeed, the synthesis of riboflavin by cer- 

 tain fungi, e.g., by Ashbya gossypii and related organisms, constitutes a 

 commercial method for the production of this vitamin.^ 



Aside from decreased growth in the absence of sufficient supplies, few 

 other effects of riboflavin deficiency in microorganisms have been described. 

 From the role of this vitamin as a hydrogen carrier, it might be expected 

 that, as in higher animals, the level of certain oxidative enzyme systems 

 would be depressed during growth on suboptimal supplies. That this is 

 true is shown by investigations of Doudoroff^ wdth the luminescent orga- 

 nism, Photohacterium phosphorescens. Cultures grown on a yeast autolyzate 

 agar frequently produced, as variants, dull or dark colonies; these lumi- 

 nesced more brightly when riboflavin was added. The same "dark" colonies 

 were stimulated in growth on a riboflavin-deficient medium by additions 

 of this vitamin. Apparently the dull variants had lost the ability to synthe- 

 size sufficient riboflavin for their needs; this was not true of the original 

 bright colonies. In this case, amounts of riboflavin sufficient for growth of 

 the "dull" variants were insufficient to permit maximum luminescence. 

 That riboflavin-enzymes are among those concerned in light production bj'' 

 such luminescent organisms has been proved by Eyring and Johnson. ^° 



At low concentrations, many fatty materials show a "sparing efl"ect" 

 on the requirement of lactic acid bacteria for riboflavin;^ this effect, which 

 is sometimes troublesome in microbiological assays, may possibly indicate 



2 E. E. Snell, F. M. Strong, and W. H. Peterson, Biochem. J. 31, 1789 (1937). 



3 E. E. Snell and F. M. Strong, Enzymologia 6, 186 (1939). 



^ E. E. Snell and F. M. Strong, Ind. Eng. Chem. Anal. Ed. 11, 346 (1939). 



s E. E. Snell, in Vitamin Methods, Vol. I, p. 327. Academic Press, New York, 1950. 



^ B. C. J. G. Knight, Vilamins and Hormones 3, 105 (1945). 



7 G. W. Beadle and E. L. Tatum, Am. J. Botany 32, 678 (1945). 



8 F. W. Tanner, Jr., C. Vojnovich, and J. M. Van Lanon, ./. Bactcriol. 58, 737 (1949). 

 9M. Doudoroff, Enzymologia 5, 239 (1938). 



i» F. H. Johnson and H. Eyring, J. Am. Chem. Soc. 66, 848 (1944). 



