SUBGROUPS AND GENERA OF THE BACTERIACEAE 47 



in a film upon the surface of the culture medium. Capable of 

 fixing atmospheric nitrogen in . considerable amounts when grown 

 in solutions deficient in combined nitrogen. Motile or non-motile, 

 if the latter, with polar flagella. 



The type species is Azotobacter chroococcum Beijerinck. 



It is possible that the demonstration of endospore production 

 by Lohnis and his co-workers will require the removal of this 

 genus to the Bacilleae. 



Subtribe IV. Bacteriinae Subtrib. nov. 



Cells not fusiform, rod shaped; not hemoglobinophilic; aerobic, 

 facultative, or microaerophilic; not securing growth energy exclu- 

 sively by the oxidation of carbonaceous compounds. Spores never 

 formed. . Motile or non-motile. 



The following key to the genera recognized gives the most 

 important differential characters: 



Key to genera of Bacteriinae 



A. Producing usually a yellowish or greenish or fluorescent pigment, usually 



Gram-negative, motile by means .of polar flagella, or non-motile. 



Genus 1. Pseudomonas 



B. When pigmented not greenish or fluorescent, when motile with peritrichous 



flagella. 



1. Cells typically pigmented, chromoparous. 



a. Producing red or pink pigment Genus 2. Serratia 



b. Producing a violet pigment Genus 3. Chromobacterium 



2. Cells not typically definitely pigmented, or at least not red or 



violet, 

 a. Cells typically Gram-negative. 



(1) Non-motile, showing bipolar staining commonly. Never 



produce gas from carbohydrates. Power of acid pro- 

 duction low Genus 4. Pasteurella 



(2) Not showing bipolar staining. 



(a) Not producing honey-like growth on potato, branch- 



ing forms uncommon. 

 X. Gelatin not liquefied or liquefied very slowly. 



Motile or non-motile Genus 5. Bacterium 



XX. Gelatin liquefied quickly. Motile. 



Genus 6. Proteus 



(b) Producing a honey -like growth on potato. Branched 



cells not unconamon. 



Genus 7. Pfeifferella 



