Jan. 28. i9i8 Nitrogen-Assimiloting BacteHa 205 



A general idea may be gained from Table XVII concerning the relative 

 increase in pigment formation in the presence of the nitrates. A study 

 of the table gives a fair idea of the relative differences in pigment pro- 

 duction. 



Very interesting results were obtained with strain A. It will be seen 

 from Table XVII that no pigment was produced in the control culture 

 after 10 days, while in the presence of nitrates pigmentation was noted. 

 The intensity of the pigment varied with the increase of nitrate up to 150 

 mgm. Beyond 150 mgm. there was no increase. Potassium and sodium 

 nitrate did not exert such a decided influence on pigment production as 

 calcium nitrate. The latter salt produced an intense dark -brown to 

 brownish-black pigment. 



In the case of strain B the influence of nitrate was not so pronounced 

 since this strain normally produced considerable pigment in the absence 

 of nitrates. Potassium and sodium nitrate caused a slight increase in 

 pigment formation. Here, again, the calcium salt brought about most 

 pronounced increase. However, the relative increase in pigment forma- 

 tion in strain B was not so pronounced as in strain A. 



Where the nitrate was present, a much more spreading growth was 

 obtained. A heavy bacterial growth accumulated at the base of the slope 

 except in the two cultures in which the highest concentrations were used. 

 In the latter instances the accumulation was less than those in cultures 

 growing en media containing no nitrate. Although the original inocula- 

 tion could not be made absolutely uniform, so far as number of organ- 

 isms was concerned; nevertheless it was evident that on those slopes 

 containing 10, 25, 50, and 100 mgm. of nitrate in 100 c. c. of the medium 

 a much more abundant growth was obtained than on those slopes free 

 from nitrate. Here, again, it is seen, in a rough, comparative way, that 

 the smaller amounts of nitrates caused an increase in the number of 

 Azotobacter. 



The results of this work on pigment production are quite in accord with 

 those of Sackett. Potassium, sodium, and especially calcium, nitrates 

 in varying amounts increase pigment formation by Azotobacter with an 

 increase in nitrate concentration. This effect is especially marked in 

 strain A, which under normal conditions does not produce any pigment. 



INFLUENCE OF NITRATES ON THE FORMATION OF VGLrUTIN BODIES IN AZOTOBACTER 



The presence of volutin bodies, or metachromatic granules, in Azoto- 

 bacter has been shown by Bonazzi (7). These substances, according to 

 Meyer {34, p. 238), are reserve food materials other than fat droplets, 

 glycogen, and similar substances reacting with iodin stain which occur 

 in the cytoplasm of the cells of various bacteria. With Millon's reagent 

 they give no reaction. He believes that these bodies are composed of 

 nucleic-acid compounds, but are not nuclear proteids. 



