THE PROTEINS OF MICRO-ORGANISMS 339 



they have the disadvantage of a bitter taste, due to acid 

 substances derived from the hops. The taste can be 

 eliminated by washing with dilute sodium carbonate. 

 Saccharomyces cerevisice does not grow very satisfactorily 

 on ammonium salts as the source of nitrogen but requires 

 expensive organic sources, so that its use for protein 

 production is not economically sound. During the 1914 

 to 1918 war the use of Torula utilis, also known as 

 Mineralhefe or Futterhefe, was developed in Germany. 

 It grows much more readily on inorganic media than does 

 Sacchxiromyces, has no bitter taste and is an effective 

 protein source for man and animals. It is usually grown 

 on molasses and ammonium salts under conditions of 

 good aeration. Yields of the organism, as dry weight, up 

 to 75 per cent, of the sugar consumed can be obtained. 

 A similar process has been worked out recently in this 

 country using a thermophilic variant of T . utilis which 

 gives an almost theoretical conversion of the nitrogen 

 supplied to protein. The protein content of the dried 

 yeast is 45 to 50 per cent. The dried product also con- 

 tains 20/xg. per gram of aneurin, 80 to 85 ju,g. per gram of 

 riboflavin and 400 to 450 /xg. per gram of nicotinic acid. 

 A fifteen-fold increase in the inoculum is obtained in 

 9 hours gro^\i:h on molasses wastes. 



It has been shown that the amino-acid, alanine, 

 CH3CH.NH2.COOH, in yields up to 65 per cent., can be 

 synthesised from pyruvic acid and ammonium salts. As 

 a result Oesterlein and Knoop suggested that amino -acids 

 in general might be synthesised by the following route : — 



/OH 



R.CO.COOH + NH3 > R.C^COOH 



^NH2 



x4mmonia condenses with a keto-acid to form the hydroxy- 

 amino-acid, whicli loses water witli formation of an 

 imino-acid : — 



