NUTRITION OF MICRO-ORGANISMS 



were also found to inhibit pantothenic acid metabolism, whilst other 

 related compounds did not ; some of these did not inhibit growth, 

 whilst others, although they inhibited growth, were unaffected by 

 pantothenic acid. Pantoyltaurine and the six other compounds that 

 inhibited pantothenic acid metabolism showed wide variations in the 

 concentrations necessary to produce inhibition, but in every instance 

 their ability to inhibit metabolism paralleled their ability to inhibit 

 growth. Similarly, the concentrations of pantoyltaurine required to 

 inhibit growth and pantothenic acid metabolism in five different 

 micro-organisms ran parallel. These observations lend further 

 support to the view that inhibition of pantothenic acid metabolism is 

 responsible for the effect of pantoyltaurine (and related compounds) 

 on growth. 28 Although low concentrations of pantoyltaurine delayed 

 the growth of haemolytic streptococci, even relatively high concen- 

 trations had no immediate effect when added to growing cultures ; 

 there was a lag of an hour or more. The action of pantothenic acid 

 in antagonising inhibition by pantoyltaurine was also a delayed one. 

 Pantothenic acid metabolism, however, was inhibited immediately by 

 pantoyltaurine both in streptococci and in C. diphtheriae, and the 

 process started again immediately the pantoyltaurine was withdrawn. 

 The metabolism of pantothenic acid normally took place in consider- 

 able excess of the needs of the organisms and, during the latent period, 

 they probably utilised materials previously made in excess. This was 

 confirmed by the observation that, when pantoyltaurine was added in 

 a concentration sufficient to inhibit pantothenic acid metabolism but 

 not to inhibit growth, growth ceased almost immediately on addition 

 of further pantoyltaurine. ^^ 



By studying the effect of various reagents on the pantothenic 

 acid content of two strains of /3-haemolytic streptococci, H. Mcllwain ^^ 

 showed that the bacterial cells normally contained 15 to 50 m/xmol. 

 of firmly bound pantothenic acid per g. of dry matter. This could 

 only be removed by autolysis or enzymic digestion, whereas loosely 

 combined pantothenic acid was readily removed by washing with 

 saline at 37° C. Pantoyltaurine did not remove the firmly bound 

 protein, and, similarly, sulphanilamide did not release firmly bound 

 j!)-aminobenzoic acid from the cells. Mcllwain therefore suggested 

 that pantoyltaurine and sulphanilamide act as bacteriostatic agents 

 by preventing the binding by susceptible bacteria of pantothenic acid 

 and ;^-aminobenzoic acid respectively in a form in which they can 

 function inside the cell. 



Moulds 



Pantothenic acid stimulated the growth of Penicillium digitatum,^^ 

 but P. chrysogenum synthesised pantothenic acid, the culture fluid 



25 385 



