208 PRINCIPLES OF SOIL MICROBIOLOGY 



Ordinary bouillon, with or without peptone, yeast water, peptone solution, 

 which have been made alkaline and to which 0.1 to 0.2 per cent of urea has been 

 added are quite suitable for the cultivation of the organisms. To study the 

 urea splitting power of the organisms, various quantities of urea may be em- 

 ployed (usually 2 per cent), but the greater the amount of urea, the greater is the 

 danger of the destructive action of the ammonium carbonate. Viehoever s used, 

 for the isolation of Bac. probalus and other urea bacteria, a medium consisting of : 



Water 1000 cc. Nad 0.1 gram 



K 2 HP0 4 1 gram FeCl 3 0.01 gram 



CaCl 2 0.1 gram Urea 20.0 grams 



MgSO i 0.3 gram Liebig's beef ex- 

 tract 5.0 grams 



Agar is added to this solution when a solid medium is wanted for the isolation 

 of the bacteria from colonies. Ammonium carbonate or urea agar are prepared 

 by adding 3 grams of the first or 3 to 30 grams of urea to a medium consisting 

 of 1500 parts of water + 30 agar + 6 peptone + 4 Liebig's beef extract + 1 NaCl 

 -I- 5 glucose. 



Classification and description. The urea bacteria include both anaero- 

 bic and aerobic forms. Miquel divided all these bacteria into two 

 general groups: (1) Urococci and (2) Urobacilli. Among the cocci 

 he observed as many as thirty different species representing four genera: 

 Urococcus, Urosarcina, Micrococcus and Planosarcina, while the Uro- 

 bacilli were also divided into various genera. 



The urea decomposing organisms can thus be divided into four groups: 



I. Spore-bearing cocci. Planosarcina vreae Beij. forms packets on solid and 

 liquid media, of 4 to 8 cells (0.7 to 1.2/*), and is motile by means of long flagella. 

 The spherical endospores (0.6m) can withstand 80°C. for ten minutes. 



II. Non-spore bearing cocci. Urococcus van tieghemi Miquel (Syn. Torula 

 ammoniacale Pasteur, Mic. ureae Cohn), 1 to 1.5^ in diameter, occurring in twos, 

 often in chains; Mic. ureae liquefaciens Flugge, Uros. hansenii Miquel and a num- 

 ber of other Urosarcinae and Micrococci described by Miquel, Rochaix and Du- 

 fourt, 9 as well as the common species Micr. pyogenes and Strept. pyogenes. 



III. Spore-bearing bacilli. These include the Urobacillus pasteurii (Miquel) 

 Beij., 1 to 1.2 by 2.5^, single or short chains, motile, forming egg-shaped endo- 

 spores, persisting in dry soil for many years, decomposing urea very actively; 

 Urob. duclauxii, Urob. freudenreichii, Urob. maddoxii and other species described 

 by Miquel; Urob. leubii Beij., Bac. probatus Vieh., Bac. ureae II and III Burri. 

 According to Lohnis, Bac. mycoides and Bac. megatherium, which decompose urea, 



8 Viehoever, A. B. Botanische Untersuchung harnstoffspaltender Bakterien 

 mit besonderer Berucksichtigung der Spezies diagnostisch verwertbaren Merk- 

 male und des Vermogens der Harnstoffspaltung. Centrbl. Bakt. 39: 209-359. 

 1913. 



9 Rochaix and Dufourt. Contribution a l'etude des urobacteries. Compt. 

 Rend. Soc. Biol. 69: 312-314. 1910. 



