40 PHARMACEUTICAL BACTERIOLOGY 



hydrogen sulphide or other sulfur compounds, the cells in consequence 

 containing neither sulfur granules nor bacterio-purpurin. The cells 

 apparently do not possess a well-organized or well-differentiated nucleus. 

 The cells are usually minute and spherical, rod-shaped or spiral in shape, 

 in most genera not producing true filaments; the filaments when formed 

 not sheathed, and frequently branching, thus being differentiated from 

 the iron bacteria. The cells may occur singly, in chains or other groupings. 

 The cells may be motile by means of flagella, or non-motile; they are never 

 notably flexuous. Cell multiplication occurs always by transverse, never 

 by longitudinal fission. Some genera produce endospores, particularly 

 the rod-shaped types. More or less branching of cells and filaments may 

 occur, reaching its maximum expression in the genera Nocardia and Acti- 

 nomyces which may show typical mycelium formation, intergrading 

 with the molds. Chlorophyll is absent, though the cells may be pig- 

 mented. The cells may be united into gelatinous masses, but never form 

 motile pseudoplasmodia nor develop a highly specialized cyst-producing 

 fruiting stage, such as is characteristic of the Myxobacteriales. 



I. Family NITROBACTERIACE.E. Fam. nov. Organisms usually 

 rod-shaped (sometimes spherical in Nitrosomonas and possibly in Azoto- 

 bacter). Cells motile or non-motile; when motile with polar, never peri- 

 trichous, flagella. Endospores never formed. Obligate aerobes, capable 

 of securing growth energy by the direct oxidation of carbon, hydrogen 

 or nitrogen or of simply compounds of these. Non-parasitic (usually 

 water or earth forms). 



1. Hydrogenomonas. Jensen, 1909. Monotrichic short rods capable 

 of growing in the absence of organic matter, and securing growth energy 

 by the oxidation of hydrogen (forming water). Kaserer (1905) who first 

 described the organism states that his species will also grow well on a variety 

 of organic substances. f 



The type species is Hydrogenomonas pantotropha (Kaserer) Jensen. 

 Nikleuski (1910) described two additional species, H. vitrea and H.flava. 



2. M ethanomonas . Jensen, 1909. Monotrichic short rods capable of 

 growing in the absence of organic matter and securing growth energy 

 by the oxidation of methane (forming carbon dioxide and hydrogen). 

 The type species is M ethanomonas methanica (Sohngen) Jensen. 



3. Carboxydomonas. Jensen, 1909. Autotrophic rod-shaped cells 

 capable of securing growth energy by the oxidation of carbon monoxide 

 (forming carbon dioxide). The type species, Carboxydomonas oligocar- 

 bophila (Beijerinck and van Delden) Jensen, is described as non-motile. 



4. Mycoderma. Persoon, 1822 emended. Synonyms: UlvinaKuetz- 

 ing 1837; Umbina Naegeli 1849; Bacteriopsis? Trevisan 1885; Gliacoc- 

 cus: Maggi 1886; Acetobacter Eurhmann 1905; Acetimonas Jensen 1909. 



