FAMILY ATHIORHODACEAE 861 



FAMILY II. ATHIORHODACEAE MOLISCH.* 



(Molisch, Die Purpurbakterien, Jena, 1907, 28; Rhodobacterioideae Buchanan, 

 Jour. Bact., 3, 1918, 471; Athiorhodobacteria Bavendamm, Ergeb. Biol., 13, 1936, 49.) 



Unicellular bacteria, of relatively small size, occurring as spheres, short rods, 

 vibrios, long rods and spirals. Motility' is due to the presence of polar flagella. 

 Gram-negative. They produce a pigment system composed of bacteriochlorophyll 

 and one or more carotenoids, coloring the cells yellowish-brown, olive brown, dark 

 brown or various shades of red. Color usually not observable with single cells but 

 only with cell masses. Generally microaerophilic, although many representatives 

 may grow at full atmospheric oxygen tension. Capable of development under 

 strictly anaerobic conditions, but only in illuminated cultures by virtue of a photo- 

 synthetic metabolism. The latter is dependent upon the presence of extraneous 

 hydrogen donors, such as alcohols, fatty acids, hydroxy- and keto-acids, and does 

 not proceed with the evolution of molecular oxygen. Those members which can 

 grow in the presence of air can also be cultivated in darkness, but only under aerobic 

 conditions. 



Key to the genera of family Athiorhodaceae. 



I. Cells rod-shaped or spherical, not spiral -shaped. 



Genus I. Rhodopseudomonas, p. 861. 

 II. Cells spiral-shaped. 



Genus II. Rhoduspirillum, p. 866. 



Genus I. Rhodopseudomonas Kluyver and van Niel emend, van Niel. 



{Includes Rhodobacillus 'Slolisch., Die Purpurbakterien, Jena, 1907, 14; Rhodobac- 

 terium 'Molisch, ibid., 16; Rhodococcus Molisch, ibid., 20; Rhodovibrio Molisch, ibid., 

 2\; Rhodocystis^ioWsch, ibid., 22; Rhodonostoc Molisch, ibid., 23; RhodosphaeraBu- 

 chanan. Jour. Bact., 3, 1918,472; Rhodorrhag us Bergey et al., Manual, 3rd ed., 1930, 

 5So; Rhodomonas Kluyver and van Xiel, Cent. f. Bakt., II Abt., 94, 1936, 397; not 

 Rhodomonas Orla-Jensen, Cent. f. Bakt., II Abt., 22, 1909, 331 ; Kluyver and van Xiel, 

 in Czurda and Maresch, Arch. f. Mikrobiol., 8, 1937, 119; van Xiel, Bact. Rev., 8, 

 1944, 86.) From Greek rhodon, red and pseudomonas, false unit. 



Spherical and rod-shaped bacteria, motile by means of polar flagella. Gram- 

 negative. Contain bacteriochlorophyll which enables them to carry out a photo- 

 synthetic metabolism. The latter is dependent upon the presence of extraneous 

 oxidizable substances and proceeds without the evolution of molecular oxygen. 

 Though some members can oxidize inorganic substrates, none appears to be strictly 

 autotrophic, due to the need for special organic growth factors. Produce accessory 

 pigments causing the cultures, especially when kept in light, to appear in various 

 shades of brownish-yellow to deep red. 



The genus includes the members of Molisch's genera Rhudobuclerium, Rhodo- 

 bacillus, Rhodovibrio, Rhodocystis, Rhodonostoc and Rhodococcus , as well as the genera 

 Rhodosphaera Buchanan, Rhodorrhagus Bergej' et al. and Rhodomonas Kluyver and 

 van Xiel. 



The type species is Rhodopseudomonas palustris (Molisch) van Xiel. 



* Completely revised by Prof. C. B. van Xiel, Hopkins Marine Station, Pacific 

 Grove, California, January, 1944. 



