BACTERIA DECOMPOSING UREA 207 



waters of Paris, fifty-two forms in the sewage waters and sixty-six in 

 the drainage of the privy closets. The urea bacteria of the surface 

 soil were found to form 1 to 2 per cent of the total number of bacteria. 

 Manure and urine contained 10 per cent of their flora as urea bacteria. 

 The air in Paris was found to contain one urea splitting organism for 

 every sixty-seven other forms. 



Urea bacteria are very abundant in the soil (p. 37). Frequently 

 the urea is so rapidly decomposed as to lead to actual losses of ammonia. 

 This can be prevented, however, by a proper mixture of the urea in the 

 soil. 3 



Methods of isolation. The isolation and cultivation of the urea bac- 

 teria does not present great difficulty. The selective and enrichment 

 cultivation 4 can be readily utilized for this purpose. 



For the purposes of isolation, two solutions have been suggested: 5 

 1. Tap water 1000 cc. 2. Tap water 1000 cc. 



K2HPO4 0.5 gram K 2 HP0 4 0.5 gram 



Calcium citrate or Ammonium 

 tartrate 10.0 grams malate 10.0 grams 



Urea 30.0 grams Urea 50.0 grams 



One hundred cubic centimeters of either solution is inoculated with 2 grams of 

 soil and incubated at 23° or 33°; in 36 to 48 hours, the medium becomes well 

 inoculated with urea bacteria. After two or three transfers, the organisms are 

 readily obtained in pure culture. A medium consisting of 50 grams of urea, 

 0.5 gram K2HPO4, 100 cc. of soil extract and 900 cc. of tap water may be used. 6 

 Peptone gelatin containing 2 to 5 per cent of urea was found to be a very good 

 solid medium. 7 A few days after inoculation, often only after twenty-four hours, 

 most of the visible colonies will be found surrounded with a halo. This is com- 

 posed of dumb-bell shaped crystals insoluble in water and consisting of carbonate 

 and phosphate of calcium which were precipitated from the medium as a result 

 of the formation of ammonium carbonate from the urea. The stronger the action 

 of the bacteria, the wider is the zone. The halo of crystals either surrounds the 

 colony to a width of several millimeters or rapidly covers, in 24 hours, the whole 

 plate. The urea organisms are thus readily recognized and are then transferred 

 upon the specific media. 



3 Littauer, F. Zersetzung des Harnstoffs im Boden. Ztschr. Pflanzenernahr. 

 Diing. 3A: 65. 1925. 



4 Beijerinck, M. W. Anhiiufungsversuche mit Ureumbakterien. Ureumspal- 

 tung durch Urease und durch Katabolismus. Centrbl. Bakt. II, 7: 33-60. 1901. 

 Duggeli. Naturw. Wochschr. 14: 305. 1915. 



5 Sohngen, N. L. Ureumspaltung bei Nichtvorhandesein von Eisweisz. Cen- 

 trbl. Bakt. II, 23: 91-98. 1909. 



6 L6hnis, 1905 (p. 120). 

 7 Miquel, 1904 (p. 206). 



