210 PRINCIPLES OF SOIL MICROBIOLOGY 



0.1 gram NaCl, 0.01 gram FeCl 3 , 20 grams urea and 5 grams Liebig's beef extract 

 per liter. On incubating for three weeks at 28°, the culture was found to contain 

 rod-shaped organisms 10/i long which formed spores l/i in size. A small amount of 

 the culture was boiled for one minute at 100° and the organism was obtained in 

 pure culture by the dilution method, using the above medium with the addition 

 of agar. The maximum acid tolerance was found to be two drops N H 2 SOi per 

 5 cc. of agar medium (| concentration of nutrients). The maximum alkalinity 

 was expressed by 2 per cent dehydrated Na 2 C0 3 (optimum 0.2 per cent) or 22 to 

 25 per cent of ammonium carbonate (optimum 0.3 per cent). The maximum 

 concentration of urea tolerated by the organism was 30 to 40 per cent, the opti- 

 mum was 3 per cent. 



Bacillus probatus A. M. et Viehoever is motile, with peritrichic flagella and 

 rounded ends; forming on ammonium carbonate or urea agar chains of 2 to 3 

 cells. The cells vary greatly in size, usually 1 by 0.4 to 0.8/t, reaching on some 

 media a size of 3 to 10 by 0.7/*. The organism is gram-positive, spore-forming, 

 aerobic. The size of the spores on the ammonium carbonate agar ranges from 

 0.5 to 1 by 0.6 to 1.2/* to almost spherical, 0.8 to 0.9/x in diameter. The spores ap- 

 pear in 3 to 4 days on the ammonium carbonate agar at 28°C., more or less 

 at the end of the cell, as drum-shaped or spindle-shaped, swollen sporangia 

 (PI. X). Development is weak on common nutrient and nutrient-glucose agar. 

 White to grayish-opalescent. Colonies are formed in three days on the car- 

 bonate or urea agar. In peptone broth containing 0.2 per cent ammonium 

 carbonate, indol, H 2 S and trimethylamine are formed. No gas is formed from 

 sugars, acid only from glucose. Ammonia is formed from nitrites. Crystals of 

 calcium carbonate and phosphate are formed on urea agar. The enzymes cata- 

 lase, urease, reductase are formed, but not oxidase or amylase. The minimum 

 temperature for growth is 3° to 5°, optimum 28° to 35°, maximum for spore- 

 formation 42° to 43°, for spore germination 45° to 47°, for growth 44° to 45°. 

 Minimum oxygen tension per liter for spore germination and growth is 4 mgm., 

 for spore formation 10 mgm. Maximum oxygen tension for spore germination 

 is about 10 atmospheres, for growth 5 atmospheres, and for spore formation 1 to 

 5 atmospheres. The spores are killed in 11.5 to 12.5 minutes at 100°C, in 9 to 10 

 hours at 80°C. 



Geilinger 14 made a detailed study of the biology of urea-decomposing 

 bacteria, with a view of preventing the rapid loss of nitrogen due to the 

 decomposition of urea in the manure pile. Only 5.6 per cent of the 

 urea organisms isolated from soil and manure were able to live and de- 

 compose urea in the absence of oxygen. Some organisms were found to 

 be obligate anaerobes and were able to thrive in the presence of a mere 

 trace of residual oxygen. A series of bacteria capable of decomposing 



14 Geilinger, H. Beitrag zur Biologie der Harnstoff vergarenden Mikro- 

 organismen, mit besonderer Berucksichtung der Anaerobiose. Centrbl. Bakt. II, 

 47: 245-301. 1917. 



