100 growth: synthesis of bacterial protoplasm 



cell-wall and becomes concentrated within the cell to an extent 

 such that the internal concentration may be over a hundred 

 times that in the medium. Gram-negative organisms do not 

 possess this capacity to concentrate amino-acids in the free 

 state inside the cell. 



(d) Organisms exacting towards growth factors: 

 Some species of bacteria are able to grow in complex media 

 such as blood-serum, yeast extract, etc., but are unable to do 

 so in a salt-ammonium-glucose medium, even if a mixture of 

 pure amino-acids is added. In such cases, fractionation of 

 the blood or yeast medium leads to the isolation of a substance 

 or substances whose presence in minute quantities is essential 

 to growth, and which is known as a " bacterial vitamin " 

 or " growth factor." Table VIII gives a list of some of the 

 bacterial growth factors that have been identified. They 

 have no common chemical nature, A simple example is 

 given by the organism Pr. vulgaris, which is unable to grow 

 in a salt-ammonia-glucose medium unless nicotinic acid or 

 nicotinic amide is added. The presence of 1 X 10~^ grm. 

 nicotinic acid per ml. medium is sufiicient to support full 

 growth. From Table VIII it can be seen that several of the 

 growth factors are either prosthetic groups or parts of pros- 

 thetic groups of proteins and enzymes, and it would seem that 

 some bacteria find difiiculty in synthesising these chemically 

 complex active groups of enzyme systems. Pr. vulgaris is 

 unable to synthesise nicotinic acid and consequently cannot 

 manufacture coenzymes I and II, essential for the action of 

 certain oxidation mechanisms. In the case of Haemophilus 

 farainfluenzae, the synthetic disability extends to the nico- 

 tinamide-nucleoside part of the coenzyme molecule, and growth 

 cannot take place in the presence of nicotinic acid or amide, 

 but only if the nucleoside or the complete coenzyme molecule 

 is added to the medium. A sub-maximal growth of this 

 organism can occur in the presence of sub-optimal amounts 

 of coenzyme in the medium, and such " deficient " organisms 

 have an impaired oxidation mechanism, in that the rate of 

 oxidation of certain substrates is considerably less than normal. 



