FAMILY ATHIORHODACEAE 



865 



Cells: Depending upon the pH of the 

 medium, cells nearly spherical, or as dis- 

 tinct rods, often devoid of motility. 

 Motility due to polar flagella. The 

 spherical cells are found in media with a 

 pH below 7; they are usually arranged 

 in chains resembling streptococci. Rod- 

 shaped cells are characteristic for media 

 with pH above 7; the higher the pH, 

 the longer the rods. Individual cells 

 slightly less than 1 micron wide, although 

 attenuated rods (about 0.5 micron in 

 width) are frequent at pH above 8, and 

 slightly swollen cells (to 1.2 microns) are 

 found in media containing sugars. 

 Length varies from 1 to 6 microns; most 

 common dimensions in approximately 

 neutral media 2 to 2.5 microns. At pH 

 above 8 abnormal growth in the form 

 of irregular filaments. Outstandingly 

 characteristic is the zigzag arrangement 

 of the cells in chains. 



Cultures in media of pH 8 or above are 

 distinctly mucoid. Gram-negative. 



Color: Anaerobic cultures develop 

 with a brown color, the shade ranging 

 from a light yellowish-brown to a deep 

 mahogany brown. When grown in the 

 presence of oxygen, the cultures are 

 dark red. Even the pigmentation of the 

 brown-colored organisms from an an- 

 aerobic 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 

 bacteriochlorophyll and carotenoid pig- 

 ments. Xo diffusible water-soluble pig- 

 ment is produced. 



Growth possible over a pH range from 

 at least 6 to 8.5, morphology becoming 

 abnormal in the alkaline media. 



Most cultures are odorless, although 

 occasionally a faint peach-like odor can 

 be detected. 



Growth is not inhibited by the pres- 

 ence of oxygen, although the pigmenta- 

 tion 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 sorbitol. In 

 media wdth 0.2 per cent glucose or fruc- 

 tose good growth is obtained. No 

 growth with mannose. Thiosulfate is 

 not, but molecular hydrogen can be, oxi- 

 dized by this species. 



Gelatin is not liquefied; of the amino 

 acids alanine and glutamic acid are satis- 

 factory substrates, while leucine is not 

 utilized. 



Distinguishing properties: Cell shape 

 and arrangement in chains; brown color 

 of anaerobic, red pigmentation of aerobic 

 cultures; abilitj^ to grovr in media with 

 0.2 per cent propionate, glucose, fruc- 

 tose, alanine and glutamic acid; failure 

 to develop with leucine, as well as with 

 ethanol, glycerol, mannitol and sorbitol 

 in the above-mentioned concentration. 



All cultures can develop anaerobically 

 in illuminated cultures by a photosyn- 

 thetic metabolism. 



Temperature optimum 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, loc. cit., Plate 

 II, fig. 9; van Niel, loc. cit., fig. 4-6, 

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

 p. 93. 



4. Rhodopseudomonas spheroides van 

 Xiel. {Rhodococcus capsulatus Molisch, 

 Die Purpurbakterien, Jena, 1907, 20 

 Rhcdococcus minor ^Molisch, ibid., 21 

 Rhodosphaera capsulata Buchanan, Jour 

 Bact., 3, 1918, 472; Rhodosphaera minor 

 Bergey et al., Manual, 1st ed., 1923, 405; 

 Rhodorrhagus minor Bergey et al.. 

 Manual, 3rd ed., 1930, 535; Rhodorrhagus 

 capsulatus Bergey et al., Manual, 3rd 

 ed., 1930, 535; van Xiel, Bact. Rev., 8, 

 1944, 95.) From Latin sphaera, a round 

 body and Greek eidos, form of. 



