CHAPTER IX 

 Bacteria Decomposing Urea, Uric and Hippuric Acids 



Urea, uric and hippuric acids are the products of protein decomposi- 

 tion in the animal organism and form the most important nitrogen con- 

 stituents of the liquid part of the manure. These compounds are not 

 directly available as sources of nitrogen to higher plants. They have to 

 be first decomposed by various groups of microorganisms existing in 

 manure and in the soil and transformed into ammonia and other com- 

 pounds. The chemical processes concerned are discussed in detail else- 

 where (p. 486). 



Organisms decomposing urea. Pasteur 1 was the first to recognize in 

 1860 that ammonia formation from urea is brought about by a living 

 organism, namely Torula ammoniacale. It was later found that organ- 

 isms capable of decomposing urea are found in most families of bacteria, 

 actinomyces and fungi, but certain specific bacteria, whose metabolism 

 is closely connected with the transformation of this substance, are 

 termed urea bacteria. These are divided into cocci and bacilli. The 

 former are usually destroyed at 60° to 70°, while the latter, due to their 

 ability to form endospores, can withstand heating at 90° to 95° for 

 several hours. The optimum temperature for the action of these organ- 

 isms is about 30°C. They usually thrive best in media containing urea 

 (2 per cent), particularly when made alkaline with ammonium carbon- 

 ate (2 to 3 grams per liter). The accumulation of ammonium carbon- 

 ate from the hydrolysis of the urea is so great, in many instances, as to 

 kill the organisms themselves. A rapid urea decomposition does not 

 necessarily accompany a rapid growth. The urea bacteria differ in 

 their oxygen tension; most of them are aerobic, although the amount of 

 oxygen required may be rather small. Many of these organisms are 

 probably varieties of some of the common soil bacteria. The urea 

 splitting bacteria are commonly found in great abundance in soil, 

 manure, dust and water. Miquel 2 found urea organisms in the canal 



1 Pasteur, L. De l'origine des ferments. Nouvelles experiences relatives 

 aux generations dites spontances. Compt. Rend. Acad. Sci. 50: 849-854. 1860. 



2 Miquel, P. Die Vergarung des Harnstoffes, der Harnsaure und der Hip- 

 pursaure. Lafar's Handb. techn. Mykol. 3: 71-85. 1904. (References to earlier 

 work.) 



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