GENERAL MORPHOLOGY AND PHYSIOLOGY 41 



Cells rod-shaped, frequently in chains, non-motile. Cells grow 

 usually on the surface of alcoholic solutions, securing growth energy by 

 the oxidation of alcohol to acetic acid. Also capable of utilizing certain 

 other carbonaceous compounds, as sugar and acetic acid. Elongated, 

 filamentous, club-shaped, swollen and even branched cells common and 

 quite characteristic. 



The type species is My coder ma aceti Thompson? 



5. Nitrosomonas. Winogradsky, 1892. Includes Nitrosococcus Win- 

 ogradsky 1892. 



Cells rod-shaped, or spherical, motile or non-motile, if motile with 

 polar flagella. Capable of securing growth energy by the oxidation of 

 ammonia to nitrates. Growth on media containing organic substances 

 scanty or absent. 



The type species is Nitrosomonas europcea Winogradsky. 



6. Nitrobacter. Winogradsky? 1892. Synonym: Nitrosobacterium? 

 Rullmann 1897. 



Cells rod-shaped, non-motile, not growing readily on organic media 

 or in the presence of ammonia. Cells capable of securing growth energy 

 by the oxidation of nitrites to nitrates. 



Winogradsky names no species, although he described one. It might 

 be termed Nitrobacter Winogradskyi and made the type species. 



7. Azotobacter. Beijerinck, 1901. Synonyms: Parachromatium Beije- 

 rinck 1903; Azotomonas Jensen 1909. 



Relatively large rods, or even cocci, sometimes almost yeast-like in 

 appearance, dependent primarily for growth energy upon the oxidation 

 of carbohydrates. Motile or non-motile; when motile, with tuft of polar 

 flagella. Obligate aerobes usually growing in a film upon the surface of 

 the culture medium. Capable of fixing atmospheric nitrogen when grown 

 in solutions containing carbohydrates and deficient in combined nitrogen. 

 The best-known free-living nitrogen-fixing bacteria of the soil. 



The type species is Azotobacter chroococcum Beijerinck. 



8. Rhizobium. Frank, 1889. Synonyms: Phytomyxa Schroeter 1886; 

 Cladochytrium Vuillemin 1888; Rhizobacterium Kirchner 1895; Pseudo- 

 rhizobium Hartleb 1900; Rhizomonas Jensen 1909. (See also p. 104.) 



Comment. Phytomyxa Schroeter has priority over Rhizobium, but 

 because of the confusion which would arise from the substitution of the 

 older correct name for the better known term Rhizobium, the committee 

 recommends the adoption of the latter. 



Minute rods, motile when young by means of polar flagella. Involu- 

 tion forms abundant and characteristic when grown under suitable 

 conditions. Obligate aerobes, capable of fixing atmospheric nitrogen 

 when grown in the presence of carbohydrates in the absence of com- 



