378 . THE NITRIFYING BACTERIA. 



205. Nitrosomonas and Nitrosoeoceus. 



Two main types of nitroso-bacteria can be differentiated in 

 consequence of the results of existing investigations. One of them 

 (in several species) is found in all the soils of the Old World 

 (Europe, Asia, Africa) hitherto examined, and is known as 

 Nitrosomonas. The second is peculiar to the soil of the two 

 remaining continents, and has received the name of Nitrosoeoceus. 

 The individual organisms of the first-named type are each provided 

 with a single cilium, and exhibit powers of locomotion which are 

 manifested at an early stage in the cultures and cause these to 

 become decidedly opalescent. Subsequently the cells become 

 quiescent and collect as zoogloea, which rest in the form of greyish 

 gelatinous clouds on the carbonate at the bottom of the liquid. 

 We will describe this (Nitrosomonas} genus first. 



Only a single species of nitroso-bacterium has been discovered 

 in European soils, viz., Nitrosomonas europcea. At the opalescent 

 stage of the culture this organism appears as briskly motile cells 

 (fitted with a short flagellum) in the shape of short rods 1.2-1.8 p 

 long and 0.91.0 ja broad. The cells of Nitrosomonas javanica, 

 cultivated from the soil of the Botanical Garden at Buitenzorg, 

 near Batavia, are globular, and only attain a diameter of 0.5-0.6 //., 

 but their flagellum is very long as much as 30 //,. The Nitroso- 

 monas japonica, found in soil from Tokio, is like the Nitrosomonas 

 africana, isolated from samples of soil from Tunis and from La 

 Reghaia, in Algeria very similar to the European species, only 

 somewhat smaller. 



Differing from these species are those of the genus Nitroso- 

 eoceus, found in South American and Australian soils. They do 

 not form zoogloea, neither are they ciliated. That obtained from 

 Quito (Ecuador) is a coccus 1.5-1.7 p in diameter. A similar 

 species, except in point of size, is the Nitrosoeoceus hrasiliensis, 

 obtained as a pure culture from the soil of Campinas (Brazil), and 

 attaining a diameter of 2 ju, ; and the species grown from Melbourne 

 soil is undistinguishable from this latter. The nitroso-bacteria 

 are, as observed by WINOGRADSKY (IX.), very susceptible to 

 desiccation, and consequently the amount of such organisms in 

 the soil decreases as drying progresses. They are almost entirely 

 lacking in the air. 



206. The Nitro-Baeteria 



differ from the species already described, not only from a chemico- 

 physiological, but also from a morphological point of view, being 

 smaller and more slender. The cells are an elongated oval, mostly 

 pear-shaped, 0.5 ^ in length and 0.15-0.25 ^ in breadth, and are 

 therefore among the smallest of all known organisms. In liquid 

 cultures they develop and congregate to form a thin, mucinous 



