270 AZOFICATION 



produced from glucose and ammonia, presumably through the 

 formation of pyruvic aldehyd and formaldehyd: 



CH 3 HN C CH 3 



I I I 



CO + 2NH 3 + HCHO = HC + 3H 2 O 



CHO N C H 



which is nearly related to the amino-acid, histidin: 



H N C CH 3 H N C CH 2 CHNH 2 COOH 



H C [ ! + CH 2 NH 2 COOH -+H O + H 2 



N C H N C H 



The various amino-acids may, through the intervention of pro- 

 teinases, condense with the formation of dipeptids, thus: 



rH 3 CHNHsCOOH + CH 3 CHNH 2 COOH = 



CH 3 CHNH 2 CONHCHCH 3 OOOH + H 2 O 



By the continuation of this process and by condensing with phos- 

 phorus and sulphur-bearing compounds, probably through the 

 intervention of other enzymes, there may result the complex protein 

 of the Azotobacter cell. 



Pigment Production by Azotobacter. Most species of Azotobacter 

 produce pigments. These vary in color from brown to black of the 

 A. chrcdcccciim to a yellow or orange of the A. vinelandn. The 

 pigmented film usually develops on the culture media in from three 

 to seven days. It is formed by A. chroococcum earlier and in more 

 abundance where old brownish cultures are used as the inoculating 

 material. The pigment is produced and retained within the bacterial 

 cell; it occurs in neither the capsule nor the medium. The pigment 

 produced by A. chroococcum is most pronounced when a dextrin 

 agar medium to which calcium carbonate is added is kept at a tem- 

 perature of 30 C. under well aerated conditions. According to 

 Jones, it is produced only when there is a lack of suitable available 

 nutrient material and when organisms in the pigmented area have 

 ceased to multiply. The color of the pigment is intensified if 

 nitrates are added to the medium in which the organism is growing. 

 The non-pigmented strains apparently fix nitrogen just as readily 

 as do those which have not lost the power of forming pigments. 



The pigment from Azotobacter chrcococcum is insoluble in water, 

 alcohol, ether, chloroform, benzol, and carbon bisulphid. It dis- 

 solves in alkalies, undergoing decomposition with the formation of 

 a dark brown solution, Sackett maintains that the peculiar brown- 

 ish color which is characteristic of certain " nitre spots" of some soils 

 is due to the pigment produced by Azotobacter. Such soils are high 



