NITROGEN METABOLISM OF BACTERIA 399 



The ability of Bacillus subtilis to break down protein in the 

 presence of fermentable sugar, and in the absence of an added 

 buffer, may be explained as follows. This organism attacks 

 glucose slowly, and for this reason it is able to produce its pro- 

 teolytic enzyme before the hydrogen ion concentration reaches 

 a point unfavorable to further growth. When the enzyme is 

 thus formed the products of the nitrogen metabolism neutralize 

 the acid, at least in a measure, and the metabolism therefore 

 continues uninterruptedly. 



It is probable that the metabolism of Bacillus coli in a glucose 

 or lactose medium in which much of the nitrogen is in a form 

 directly available for utilization by the organism is such as to 

 maintain a hydrogen ion concentration suitable for normal 

 development without the aid of a buffer. In a case like this 

 the nitrogen metabolism is rapid enough to neutralize the acid 

 formed from the sugar decomposition. Such a condition has 

 been shown in cultures of Bacillus coli in lactose media to. which 

 tryptophan was added (Distaso, 1913). Indol production could 

 be demonstrated easily. 



A recent experiment in which the metabolism of Bacillus 

 cloacae was investigated clearly indicates that this organism be- 

 haves as Bacills subtilis does, except that the sugar is fermented 

 more rapidly by the former. The final products of glucose 

 and lactose fermentation by Bacillus cloacae are largely carbon 

 dioxide and hydrogen, and hence the hydrogen ion concentra- 

 tion is not altered greatly. 



The four organisms, B. subtilis, B. cloacae, B. coli and P. 

 vulgaris, illustrate three distinct types of metabolism. Bacillus 

 subtilis attacks protein in the presence of fermentable sugar, 

 because the sugar is fermented slowly and the nitrogen and 

 carbohydrate metabolism are maintained in equilibrium. Bacil- 

 lus cloacae is also able to regulate its own environment, although 

 the sugar is fermented very rapidly, but comparatively little 

 acid occurs among the end products, and hence bacterial devel- 

 opment and a nitrogen metabolism are not inhibited. Bacillus 

 coli and Proteus vulgaris rapidly ferment glucose with the forma- 

 tion of large amounts of acid. Providing there is sufficient 



