70 ORDER I. PSEUDOMONADALES 



Ecuador; Campinas, Brazil; and Melbourne, Habitat: Presumably widely distributed 



Australia. in soil. 



Genus III. Nitrosospira Winogradsky, 1931. 



(S. Winogradsky, Compt. rend. Acad. Sci., Paris, 192, 1931, 1004; S. Winogradsky 

 and H. Winogradsky, Ann. Inst. Past., 50, 1933, 394 and 406.) 



Ni.tro.so.spi'ra. M.L. nifrosus nitrous; Gr. spira a coil, spiral; M.L. fem.n. Nitrosospira 

 nitrous spiral. 

 Cells spiral-shaped. Oxidize ammonia to nitrite very slowly. 

 The type species is Nitrosospira briensis S. Winogradsky and H. Winogradsky. 



1. Nitrosospira briensis S. Winogradsky Habitat: Presumably widely distributed 



and H. Winogradsky, 1933. (Ann. Inst. in soil. 

 Pasteur, 50, 1933, 407.) 



bri.en'sis. French Brie, place name; M.L. 2. Nitrosospira antarctica S. Wino- 



adj. briensis of Brie. gradsky and H. Winogradsky, 1933. (Ann. 



Spirals wound tightly to form very small Inst. Past., 50, 1933, 407.) 



cylinders as long as 15 to 20 microns. Short ant. arc 'tic. a. Gr. anti opposite; Gr. arcius 



spirals have the appearance of short rods a bear; Gr. adj. antarcticus opposite the 



and ellipsoidal cells. Small pseudo-cocci ob- bear, antarctic, 



served in old cultures. Cells and colonies similar to those of N . 



Colonies on silica gel: Small, occasionally briensis except that the cells are generally 



containing cyst-like aggregates of cells. The wound together to form more compact 



cysts are more poorly developed than in spirals. 



Nitrosocystis. Aerobic. 



Aerobic. Optimum pH, between 7.0 and 7.2. 



Optimum pH, between 7.0 and 7.2. Source: Soil from the Antarctic. 



Source: Uncultivated pasture soil of Brie, Habitat: Presumably widely distributed 



France. in soil. 



Genus IV. Nitrosocystis Winogradsky, 1931. 



(S. Winogradsky, Compt. rend. Acad. Sci., Paris, 192, 1931, 1003; also see S. Winogradsky 

 and H. Winogradsky, Ann. Inst. Past., 50, 1933, 394 and 399.) 



Ni.tro.so.cyst'is. M.L. adj. nitrosus nitrous; Gr. noun cystis bladder, cyst; M.L. fem.n. 

 Nitrosocystis nitrous cyst. 



Cells ellipsoidal or elongated, uniting in compact, rounded aggregates surrounded by a 

 common membrane to form cysts. The cysts disintegrate to free the cells, particularly when 

 transferred to fresh media. Within the cyst the cells are embedded in slime. Ammonia is 

 oxidized to nitrite at a rate intermediate between that of Nitrosoijionas and that of Nitroso- 

 spira. 



Winogradsky and Winogradsky (ibid., 393) differentiated between Nitrosomonas and 

 Nitrosocystis in that the former produced soft (or clear) colonies and the latter produced 

 hard (or dark) colonies on silica gel. However, Kingma Boltjes (Arch. Mikrobiol., 6, 

 1935, 79) was able to obtain both hard and soft colonies in cultures of Nitrosomonas derived 

 from single-cell isolates. Meiklejohn (Nature, 168, 1951, 561 ; also see Jour. Soil Sci., 4, 1953, 

 62), furthermore, states that the appearance of hard or soft colonies is dependent upon the 

 density of the silica gel and upon whether the colonies are in the gel or on the surface; 

 consequently she regards Nitrosocystis as probably identical with Nitrosomonas. Some ob- 

 servers (Imsenecki, Nature, 157, 1946, 877; and Grace, Nature, 168, 1951, 117; also see 

 Riassunti d. Comunicazione, VI Cong. Internaz. d. Microbiol., Roma, 1, 1953, 53) have 



