NITROGEN METABOLISM 



217 



failure to grow. Esch. coli and " trained " Eberthella 

 typhosa can synthesise tryptophane from ammonia and 

 carbohydrates ; B. anthracis and Staphylococcus aureus 

 need amino -acids, whilst untrained E. typhosa, C. 

 diphtherice, CI. sporogenes, CI. hotulinum, etc., need 

 tryptophane preformed. For the growth of E. typhosa 

 or C. diphtherice indole can replace tryptophane, but 

 derivatives such as indole -acrylic acid, indole-acetic 

 acid or indole -propionic acid cannot. Staphylococcus 

 aureus cannot convert indole to tryptophane. 



Some amino-acids may be toxic unless an adequate 

 concentration of others is present ; for example, glycine, 

 3-alanine, serine and threonine are toxic to Str. lactis 

 in the presence of very small amounts of « -alanine, but 

 not if larger amounts are present. 



The toxic effect of leucine, 



CH.NH,.COOH, 



I 



CH 



CH, CH, 



threonine. 



or a-aminobutyric acid. 



CH-NHa-COOH, 



I 

 CH 



/ \ 

 OH CH3 



[n 



H CH3 



on B. anthracis can l^e eliminated by valine, 



CH.NH2.c00H, 



CH 



CH, 



CH, 



