602 NITROSOMONAS 



Agar Plate. — 2 days at 25° C. Round, 1 mm. in diameter, low convex, greyish-yellow 

 transparent colonies with smooth, gUstening surface and lobate edge ; structure 

 amorphous ; consistency butyrous ; easily emulsifiable. Differentiated into a 

 smooth, raised, darker centre, and a thin, effuse, radiate periphery. Some strains 

 are said to form mucoid colonies, consisting of bacilh embedded in a mucinous 

 material which appears to consist of a carbohydrate material, yielding glucose on 

 inversion (Kramar 1921). 



Agar Slope. — 2 days at 25° C. Moderate, partly confluent, shghtly raised, greyish-yellow, 

 translucent growth, with gUstening, beaten-copper surface, and finely lobate edge. 



Gelatin Stab. — 5 days at 20° C. Moderate, fihform growth extending to bottom of tube ; 

 shght surface growth 1 mm. in diameter ; no liquefaction except in very old cultures. 



Broth. — 2 days at 25° C. Poor growth with shght turbidity, and shght powdery deposit 

 disintegrating on shaking. 5 days ; moderate turbidity, shght surface ring growth, 

 and moderate viscous deposit giving rise on shaking to dense turbidity. 



Loejflers Blood Serum. — 6 days at 25° C. Abundant, mostly confluent, raised, chrome- 

 yellow growth, shghtly tinged with pink ; smooth glistening surface. Medium not 

 coloured ; no digestion. 



Potato.— % days at 25° C. Poor, effuse, confluent, whitish-pink growth, with smooth, 

 moist, ghstening surface ; medium not coloured, or coloured shghtly grey. 



Resistance. — Killed at 60° C. in 1 hour. Resists drying and freezing. 



Metabolic— Aevohic. No growth anaerobically on agar, but moderate growth in broth. 

 Opt. temp. 25° C. Pigment yeUowish-pink, not marked, on certain media only. 



Biochemical. — No acid or gas in glucose, maltose, mannitol, lactose, sucrose or salicin. 

 Indole—. M.R. — . V.P. — . Nitrate reduction — . Catalase-|-. M.B. reduc- 

 tion-}-. NH3-I-. HgS shght-}-. L.M. acid and clot in 21 days. Capable of 

 fixing atmospheric nitrogen in the presence of carbohydrates and in the absence 

 of combined nitrogen. 



Antigenic Structure. — Can be divided by agglutination into numerous different groups. 



Pathogenicity.- — Nil to man or animals. Produces nodules upon the roots of the Legu- 

 minosce. 



NITROSOMONAS 

 Definition. — Nitrosomonas. 



Cells rod-shaped or spherical, motile or non-motile ; motile forms possess polar 

 flagella. Capable of securing growth energy by the oxidation of ammonia to 

 nitrites. Growth on media containing organic substances is scanty or absent. 

 Type species. Nitrosomonas europcBa, Winogradsky. 



Winogradsky (1890a, b, c), finding that nitrification did not occur in a medium 

 containing organic matter, seeded with soil, prepared the following solution : 



Ammonium sulphate ...... 1 gm. 



Potassium phosphate . . . . . . 1 ,, 



Pure water 1000 „ 



To each 100 ml. was added 0-5-1 -0 gm. of basic magnesium carbonate ; when 

 this medium was inoculated with soil, nitrification occurred satisfactorily, the 

 ammonia being oxidized to nitrite. Five different types of organisms were found ; 

 one of them, which grew around the particles of carbonate at the bottom of 

 the flask, failed to grow in gelatin on transplantation, but could be cultivated 

 in a purely inorganic medium. This organism was obtained in pure culture, 

 and was found to be responsible for nitrification. Morphologically it consists 



