NUTRITION OF MICRO-ORGANISMS 



Penicillium digitatum, the effect being more pronounced above pK 6-5 

 than at pYL 3-0.^^ Other moulds which required biotin were Ascoidea 

 rubescens, Ophiostoma fagi, 0. piliferum and Mitrula paludosa}"^ 



Some fungi, however, can synthesise biotin. For example, Phyco- 

 myces blakesleeanus on a synthetic medium containing asparagine and 

 glucose produced a good deal of biotin, the greater part of which 

 accumulated in the medium. ^^ The yield of biotin increased with 

 tem.perature, with the amount of asparagine and in presence of traces 

 of certain metals. Penicillium chrysogenum also synthesised biotin, 

 although only in small amounts. ^^ Desthiobiotin was a normal inter- 

 mediate in the biosynthesis of biotin by this mould.^* 



An organism that cannot synthesise biotin will grow in a synthetic 

 medium if this is also inoculated with an organism that synthesises 

 biotin, and it is even possible for each of the organisms to supply the 

 other with an essential growth factor that it cannot itself produce. 

 This is believed to account for the phenomenon of symbiosis. 



Bacteria 



Biotin was essential for the growth of Lactobacillus helveticus ^^ and 

 L. arabinosus ^® and indeed for all species of Lactobacilli tested by 

 Rogosa et al}"^ Unlike yeasts, however, these organisms cannot 

 utiUse desthiobiotin in place of biotin.^® L. helveticus can utilise the 

 methyl ester of biotin, though growth and fermentation were slower 

 than with free biotin. ^^ Three strains of Leuconostoc, L. mesenteroides, 

 L. dextranicum and L. dextranicum elai, required biotin for growth 

 when the medium contained invert sugar, glucose or fructose, but 

 grew without biotin on a sucrose medium. ^^^ Biotin was also essential 

 for B. radicicola,^^' ^^ Rhizobium trifolii,^^* ^^ Staphylococcus aureus,^^ 

 Streptobacterium plantarumP and four species of Propionibacteria.^^ 

 It was also necessary for maximum growth of Clostridium tetani,^^ 

 CI. botulinum,^^ CI. kluyveri,^'^ three strains of CI. acetobutylicum,^^ 

 and about twenty other species of Clostridia.^^ B. polymyxa required 

 only biotin of the vitamin B complex, whilst B. macerans and B. 

 acetoaethylicus required both biotin and aneurine.^*^ Biotin was 

 apparently the only growth factor required by Neisseria sicca. ^'^ 



The biotin requirements of bacteria can be observed by the effects 

 of avidin on their growth. ^^ 



A biotin-deficient mutant of E. coli was isolated by C. H. Gray 

 and E. L. Tatum.^^ 



The amount of biotin present in the five bacteria, Aerobacter 

 aerogenes, Serratia marcescens, Pseudomonas fluorescens, Proteus vul- 

 garis and Clostridium butylicum ranged from 420 to 1800 molecules 

 per cell and the rate of synthesis from o-o8 to 3-2 molecules per cell 

 per second.^* 



439 



