104 GENERAL SYSTEMATIC BACTERIOLOGY 



Key to Families of the Order Eubacteriales 



1. Organisms obligate aerobes, using oxygen for direct oxidation of carbon, 



hydrogen, or nitrogen or compounds of these. Cells usually rod-shaped, 

 occasionally spherical Nitrobacteriaceae 



2. Not securing growth energy as under I. 



a. Cells spherical Coccaceae 



aa. Cells not spherical. 



b. Cells spiral Spirillaceae 



bb. Cells straight rods. 



c. Not producing endospores. Cells motile or non-motile. 



Bacteriaceae 

 cc. Producing endospores Bacillaceae 



Key to the Tribes and Genera of the Family Nitrobacteriaceae 



1. Organisms oxidize simple compounds of carbon and nitrogen. 



Nitrobactereae 



a. Cells capable of securing growth energy by the oxidation of hydrogen to 



form water Hydrogenomonas 



b. Cells oxidize methane to form CO2 and water. 



Meihanomonas 



c. Cells oxidize CO to form CO2 Carboxydomonas 



d. Cells oxidize ammonia to form nitrites Nitrosomonas 



e. Cells oxidize nitrites to nitrates Nitrobacter 



f. Cells oxidize alcohol to form acetic acid Acetobacter 



g. Cells oxidize compounds of sulphur Thiobacillus 



2. Organisms capable of fixing free nitrogen of the air. 



Azotobactereae 



a. Cells capable of fixing free atmospheric nitrogen when growing in solu- 



tions of carbohydrates Azotobacter 



b. Cells capable of fixing free nitrogen when growing symbiotically on the 



roots of Leguminosae Rhizobium 



Key to the Tribes of the Family Coccaceae 



I. Strict parasites, failing to grow or growing very poorly on usual artificial 

 media. Cells normally in pairs, occasionally in tetrads. 



Neissereae 

 II. Parasites (except Leuconosioc) growing best in media containing serum. 



Occur in pairs or chains Streptococceae 



III. Facultative parasites or saprophytes. Cell aggregates of groups, packets 

 or zoogleal masses. Growth abundant Micrococceae 



Key to the Genera of the Tribe Neissereae 

 One genus only: Neisseria. 



