V. RESPIR.\TION AT THE EXPENSE OF MINER.AL 



SUBSTANCES 



I. NITRIFYING BACTERIA 



Through the pioneer researches of S. Winogradski there were 

 discovered bacteria which grow well in purely mineral media 

 and which effect peculiar transformations of materials. Of all 

 these forms the nitrifying bacteria are especially striking 

 because they can be cultivated in pure cultures only in the 

 absence of organic compounds. According to Winogradski 

 and Omehanski^ the growth of nitrifying bacteria is checked or 

 prevented by the following quantities of various organic 

 substances: 



Nitrosomonas 



Europaea Nitrobacter 



Growth Growth Growth Growth 



Organic Substance Checked Prevented Checked Prevented 



Glucose 0.025 0.05 0.05 0.2 



Peptone 0.025 0.2 0.8 1.25 



Asparagine 0.025 0.3 0.05 0.5 



Glycerine 0.2 0.05 i.o 



Ammonia 0.0005 0.015 



The isolation of pure cultures of the nitrifying bacteria can 

 be done only by the use of silicic acid jelly or strong paper 

 plates, for neither gelatine nor agar permits a growth of these 

 most peculiar organisms. 



The nitrifying bacteria effect a vigorous formation of nitrate 

 from ammonium salts and Nitrosomonas or Nitrosococcus 

 oxidises ammonia to nitric acid, although Nitrobacter completes 

 the process in that it oxidises HNO2 to HNO3. Both reactions 

 are exothermic: 



(I) 2NH3 + 30.2 = 2HNO0 + 2H0O + 158 Cal. 



(II) 2HNO2 + Oo = 2HNO3 + 43-2 Cal. 



1 Winogradski, S. und W. Omelianski. Zentralbl. f. Bakt.. Parasitenk. u. Infektions- 

 krankh. (II). 5: 338, 377. 429. 1899; cf. also Meyerhof, O. Arch. ges. Physiol. 165: 229. 

 1916; 166: 240. 1917. 



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