FAMILY II. ATHIORHODACEAE 



57 



the form of irregular filaments. Outstand- 

 ingly characteristic is the zigzag arrange- 

 ment of the cells in chains. Gram-negative. 



Cultures in media of pH 8 or above are 

 distinctly mucoid. 



Color: Anaerobic cultures develop with a 

 brown color, the shade ranging from a light 

 3'ellowish l^rown to a deep mahogany- 

 brown. When grown in the presence of oxy- 

 gen, the cultures are dark red. Even the pig- 

 mentation of the brown-colored organisms 

 from an anaerobic culture can be changed 

 into a distinct red by shaking a suspension 

 with air for some hours; light enhances the 

 rate of this color change. Color due to bac- 

 teriochlorophyll and carotenoid pigments. 

 No diffusible water-soluble pigment is pro- 

 duced. 



Growth possible over a pH range from at 

 least 6 to 8.5, morphology becoming abnor- 

 mal in the alkaline media. 



Most cultures are odorless, although occa- 

 sionally a faint peach-like odor can be de- 

 tected. 



Growth is not inhibited by the presence of 

 oxygen, although the pigmentation is 

 thereby affected. 



Fatty acids and most substituted acids 

 are satisfactory substrates. Rapid and 

 abundant growth with propionate at a 

 concentration of 0.2 per cent. At this same 

 concentration glutaric acid leads, at best, to 

 very meager cultures, while tartrate, citrate 

 and gluconate fail to induce growth, as do 

 also ethanol, glycerol, mannitol and sorbi- 

 tol. In media with 0.2 per cent glucose or 

 fructose good growth is obtained. No growth 

 with mannose. Thiosulfate is not, but 

 molecular hydrogen can be, oxidized by this 

 species. 



Gelatin is not liquefied; of the amino 

 acids, alanine and glutamic acid are satis- 

 factory substrates while leucine is not uti- 

 lized. 



Distinctive characters: Cell shape and 

 arrangement in chains; brown color of 

 anaerobic, red pigmentation of aerobic cul- 

 tures; ability to grow in media with 0.2 per 

 cent propionate, glucose, fructose, alanine 

 and glutamic acid; failure to develop with 

 leucine, as well as with ethanol, glycerol, 

 mannitol and sorbitol in the above-men- 

 tioned concentration. 



All cultures can develop anaerobically in 

 illuminated cultures by a photosynthetic 

 metabolism. 



Thiamin is required for growth; u few 

 strains require biotin and nicotinic acid in 

 addition (Hutrier). 



Optimum temperature distinctly lower 

 than for Rhodopseudomonas palustris, and, 

 as a rule, around 25° C. 



Habitat: Regularly found in stagnant 

 bodies of water and in mud. 



Illustrations: Molisch, op. cit., 1907, 

 Plate II, fig. 9; van Niel, op. cit., 1944, fig. 

 4-6, p. 19; fig. 27-32, p. 92; and fig. 33-38, p. 

 93. 



4. RhodopseudonionaH spheroides van 



Niel, 1944. {Rhodococcus capsulatus Molisch, 

 Die Purpurbakterien, Jena, 1907, 20; Rhodo- 

 coccus minor Molisch, ibid., 21; van Niel, 

 Bact. Rev., 8, 1944, 95.) 



sphe.ro. i'des or sphe.roi'des. Gr. adj. 

 sphaeroides globular. 



Cells generally single, nearly spherical, 

 diameter without slime capsule variable, de- 

 pending upon medium, ranging from 0.7 to 

 4 microns. In young cultures actively motile 

 by means of polar flagella; motility soon 

 ceases in media which are or become alka- 

 line. Copious slime production in media at 

 pH above 7. In strongly alkaline cultures 

 abnormal cell-shapes occur in the form of 

 irregular, swollen and distorted rods, often 

 having the appearance of spore-bearing 

 cells, simulated by the production of fat 

 bodies. In sugar-containing media egg- 

 shaped cells, measuring as a rule 2.0 to 2.5 

 by 2.5 to 3.5 microns, are frequently found. 

 Gram-negative. 



Color: Anaerobic cultures develop with 

 brown color, ranging in shade from a light, 

 dirty greenish brown to a dark brown. Cul- 

 tures grown in the presence of oxygen are 

 distinctly red. As in the case of Rhodopseudo- 

 monas capsulata, the brown color of an 

 anaerobic culture can be changed to red by 

 shaking with air, light stimulating the color 

 change. Color due to bacteriochlorophyll 

 and carotenoid pigments. The large major- 

 ity of cultures of this species produce, in 

 addition, a water-soluble, non-carotenoid, 

 bluish red pigment which diffuses into the 

 culture medium. 



