XIII. UEQUIKKMENTS 6l7 



butylicumS'^- •'" B. maccrans and B. acctocthylicus require thiamine and biotin, 

 B. polyiuijxa only biotin of the vitamin B complex.^- For Neisseria sicca 

 biotin is apparently the only growth factor required. ^^ 



The essential character of biotin for a given bacterial species may be 

 studied by the effect of avidin added to the medium in an amount sufficient 

 to bind all available biotin. Xo growth will indicate that biotin is an essen- 

 tial nutrient for the microorganism in question. Several homologs, pre- 

 cursors, or in particular oleic acid and related acids (see p. 504) will support 

 growth for a large number of bacteria, even in the absence of biotin, or at 

 least they will materially fill the requirement for biotin. 



A number of bac-teria are able to synthesize biotin. The amount of biotin 

 found in the five bacteria, Aerobacter aerogenes, Serratia marcescens, Pseudo- 

 monas fluorcscens, Proteus vulgaris, and Clostridium butylicum, was calcu- 

 lated to range from 420 to 1800 molecules per cell.^^ 



C. INSECTS 



Optimal growth was maintained only in the presence of biotin in Tri- 

 bolium confusumj^''''^^ Sitodrepa panicea, Lasioderma serricorne, and Ptinus 

 lectiis.^^ Biotin is apparently not required by Silvanus surinamensisP Tri- 

 bolium can utilize not only biotin but the diaminocarboxylic acid pre- 

 pared from biotin. The sterilized larvae of Lasioderma have shown less 

 satisfactory growth in the absence of biotin than have normal larvae. 

 Thus, in the absence of symbionts biotin may become a more important 

 nutrient.^" The mosquito larvae {Aedes aegypti) require biotin for their 

 growth. It may, however, be replaced by oleic acid or lecithin.'**- ■*- 



The addition of raw egg white or avidin to the diet of the larvae of 

 Corcyra cephaloneca (rice moth) inhibited growth and caused death of the 

 larvae in 28 days. Biotin added to the diet, even 14 days after feeding with 



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'" R. Reyes-Teodoro and M. X. MicheLson, .1/t/(. Biochcm. 4, 291 (1944). 



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« W. Trager, ./. Biol. Chem. 176, 1211 (1949). 



« L. Golberg, B. de Meillon, and M. Lavoipierre, J. Exptl. Biol. 21, 90 (1945). 



