862 MANUAL OF DETERMINATIVE BACTERIOLOGY 



Keys to the species of genus Rhodopseudomonas. 



I. Based upon morphological characters. 



1. Cells clearly rod-shaped in all media. 



a. Cells short, somewhat curved, to long branched rods, size of young and 

 short cells 0.6 to 0.8 by 1.2 to 2 microns; in older cultures up to 10 mi- 

 crons long; do not form slime; liquid cultures, when young, or after 

 shaking, evenly turbid. Color red to dark brown-red. 



1. Rhodopseudomonas palustris. 



aa. Cells slender rods, 0.5 by 1.2 microns usually clumped together in exten- 

 sive slime masses. Cultures pale brown to peach-colored. 



2. Rhodopseudomonas gelatinosa. 



2. Cells more or less spherical in media at pH below 7. 



a. In media at pH about 7 clearly rod-shaped, 1 by 1 to 2.5 microns. Chains 

 of cells frequent, and in characteristic zigzag arrangement. 



3. Rhodopseudomonas capsulatus . 



aa. In media at pH above 7 cells still predominantly spherical, 0.7 to 4 mi- 

 crons in diameter. Mostly single, little tendency to chain formation. 



4. Rhodopseudomonas spheroides. 



II. Based chiefly on physiological properties. 



1. Gelatin liquefied. 



2. Rhodopseudomonas gelatinosa. 



2. Gelatin not liquefied. 



a. Does not produce mucus in media at pH above 8. Color the same under 

 aerobic and anaerobic conditions of growth. 



1. Rhodopseudomonas palustris. 

 aa. Produce mucus in media at pH above 8. Color brown in anaerobic, red 

 in aerobic culture. 



b. Develops readilj' in media with 0.2 per cent propionate as the chief 

 oxidation substrate. Mucus production marked at pH above 8, 

 but very limited between 7 and 8. 



3. Rhodopseudomonas capsulatus. 



bb. Does not develop in media with 0.2 per cent propionate as the main 

 oxidation substrate. Slime formation extensive at pH above 7. 



4. Rhodopseudomonas spheroides. 



III. Based principally upon biochemical characters. 



1. Thiosulfate used as main oxidation substrate. 



1. Rhodopseudomonas palustris. 



2. Thiosulfate not used. 



a. Propionate (0.2 per cent) used. 



3. Rhodopseudomonas capsulatus. 

 aa. Propionate not used. 



b. Mannitol and sorbitol (0.2 per cent) used. 



4. Rhodopseudomonas spheroides. 

 bb. Mannitol and sorbitol not used. 



2. Rhodopseudomonas gelatinosa. 



