BACTERIAL NUTRITION: FURTHER STUDIES ON 



THE UTILIZATION OF PROTEIN AND 



NON-PROTEIN NITROGEN 



NATHAN BERM4N and LEO F. RETTGER 



From the Sheffield Laboratory of Bacteriology and Hygiene, Yale University 



Received for publication July 1, 1917 



It has been demonstrated by independent investigators 

 (Bainbridge, 1911, and Sperry and Rettger, 1915) that bacteria 

 are unable to bring about the decomposition of native or un- 

 changed proteins by direct action. These proteins can serve as 

 food material for bacteria only through the agency of cleavage- 

 producing substances like acids, alkalies and proteolytic enzymes. 

 Even the most active gelatin-hquefying and putrefactive organ- 

 isms die from inanition in a medium which contains egg albumin, 

 serum albumin or the vegetable protein, edestin, as the only 

 possible source of nitrogen. 



It has been shown further by Rettger, Berman and Sturges 

 (1916) that egg albumin which has been coagulated by heat 

 still retains its resistance to direct bacterial action, and that the 

 proteoses and the higher or more complex polypeptids or peptone 

 fractions of Witte's ''peptone" apparently show the same indif- 

 ference to microbic influence. 



The existence of an erepsin-Hke enzyme in certain bacteria was 

 clearly indicated in the experiments of the writers (1916) which 

 have been conducted on nitrogen utilization in Witte's peptone. 

 The peptolytic enzyme elaborated by the Coli-typhi-paratyphi 

 group and by other gelatin-non-hquefying organisms studied is 

 decidedly weak, and differs further from erepsin of the animal 

 body by its inability to attack casein. At least two weeks 

 were required in the earlier tests to bring about a noticeable 

 reduction in the amount of biuret-giving substances in Witte's 



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