90 ORDER I. PSEUDOMONADALES 



fluorescent, diffusible pigments of a greenish, bluish, violet, lilac, rose, yellow or other 

 color. Sometimes the pigments are bright red or yellow and non-diffusible; there are many 

 species that fail to develop any pigmentation. The majority of species oxidize glucose to 

 gluconic acid, 2-ketogluconic acid or other intermediates. Usually inactive in the o.xidation 

 of lactose. Nitrates are frequently reduced either to nitrites, ammonia or to free nitrogen. 

 Some species split fat and/or attack hydrocarbons. Many species are found in soil and 

 water, including sea water or even heavy brines. Many are plant pathogens; verj^ few are 

 animal pathogens. 



The borderline between the straight rods found in Pseudomonas and the curved rods 

 found in Vibrio is not sharp : occasionally curved rods ma.y occur in species that normally 

 are composed of straight rods, this variation sometimes being dependent upon the medium 

 used. Recently, however, Shewan, Hodgkiss and Liston (Nature, 173, 1954, 208) have de- 

 scribed a method employing antibiotics and a vibriostatic agent whereby a sharper differen- 

 tiation between pseudomonads and vibrios may possibly be effected. Future studies of this 

 nature may show that some of the species in the genus Pseudomonas should be transferred 

 to the genus Vibrio, and vice versa. 



The type species is Pseudomonas aeruginosa (Schroeter) Migula. 



Key to the species of genus Pseudomonas. 



I. Soil and water forms. A few species are pathogenic to warm- and cold-blooded verte- 

 brates. 

 A. Soil and fresh-water forms (a few are pathogenic). 



1. Produce diffusible pigments, usually of a yellow, green or blue color; may be 

 fluorescent. (Soluble pigments are not formed in all media. Furthermore, the 

 ability to produce such pigments may be lost. Therefore, failure to observe sol- 

 uble-pigment formation does not preclude identity with species listed in this 

 category.) 



a. Grow in gelatin. 



b. Gelatin liquefied. 



c. Polar flagellate. 



d. Grows readily at 42°C. on ordinary media, 

 e. Milk becomes alkaline. 



1. Pseudomonas aeruginosa. 

 ee. Milk acidified. 



2. Pseudomonas pseudomallei. 

 dd. Grow poorly or not at all at 42° C. 



e. Grow readily at 37° C. 



f. Not known to attack cellulose. 



g. Milk becomes alkaline, indole not produced. 



3. Pseudomonas reptilivora. 

 gg. Milk acidified, indole produced. 



4. Pseudomonas caviae. 



ggg. Action on milk and indole production unre- 

 corded. 



5. Pseudomonas horeopolis. 

 ff. Attack cellulose. 



g. Milk becomes alkaline, coagulated and pep- 

 tonized, and litmus is reduced. 



6. Pseudomonas effusa. 

 gg. No growth in milk. 



7. Pseudomonas ephemerocyanea. 



