838 MANUAL OF DETERMINATIVE BACTERIOLOGY 



Suborder III. Rhodobacteriineae Breed, Murray and Kitchens.* 



(Family Rhodobacteriaceae Migula, Syst. d. Bakt., 2, 1900, 1042; Breed, Murray 

 and Kitchens, Bact. Rev., 8, 1944, 257.) 



Cells spherical, rod-, vibrio-, or spiral -shaped. Size of individual cells from less 

 than 1 to over 20 microns. Motility, when exhibited, due to the presence of polar 

 flagella. Gram-negative so far as known. No endospores formed. Red, purple, 

 brown or green bacteria which contain bacteriochlorophyll or other chlorophyll-like 

 green pigments, and usually also possess one or more carotenoid pigments. Capable of 

 carrying out a photosynthetic metabolism which differs from that of green plants in 

 that it does not proceed with the evolution of oxygen, and depends upon the presence 

 of extraneous o.xidizable compounds which are dehydrogenated with the simultaneous 

 reduction of carbon dioxide. As oxidizable substrates a variety of simple substances 

 can be used, such as sulfide, or other reduced sulfur compounds, molecular hydrogen, 

 alcohols, fatty acids, hydroxy- and keto-acids, etc. All can be grown in strictly 

 anaerobic cultures when illuminated. Those members which can grow in the pres- 

 ence of air can also be cultured in the dark under aerobic conditions. Color depends 

 markedly on environmental conditions; small individuals appear colorless unless 

 observed in masses. May contain sulfur globules. Described species have largely 

 been found in fresh water habitats. Some species occur in marine habitats. 



Key to the fatnilies of suborder Rhodobacteriineae. 



I. Purple bacteria whose pigment system consists of bacteriochlorophyll and vari- 

 ous carotenoids capable of carrying out a photosynthetic metabolism. 



A. Contain sulfur globules in the presence of hydrogen sulfide. The sulfur purple 



bacteria. 



Family I. Thiorhodaceae, p. 841. 



B. Do not contain sulfur globules even in the presence of hydrogen sulfide. All 



require organic growth factors. The non-sulfur purple and brown bacteria. 



Family II. A thiorhodaceae, p. 861. 

 II. Green sulfur bacteria containing a pigment system which has the characteristics 

 of a chlorophyllous compound although it differs from the chlorophyll of green 

 plants and from the bacteriochlorophyll of the purple bacteria. 



Family III. Chlorobacteriaceae, p. 869. 



The organisms previously included in the order Thiobacterialcs Buchanan do not 

 constitute a taxonomic entity; they represent rather a physiological-ecological com- 

 munity. In this sense, however, a special treatment of this group as a unit has de- 

 cided advantages from a determinative point of view. 



When first proposed as a systematic assemblage, the order Thiobacleria Migula 

 (Syst. d. Bakt.,^, 1900, 1039) was intended to include the morphologically conspicuous 

 organisms which, in their natural habitat, contain globules of sulfur as cell inclusions. 

 Since Winogradsky (Beitr. z. Morph. u. Physiol, d. Bact., I, Schwefelbacterien, 1888) 

 had elucidated the function of hydrogen sulfide and of sulfur in their metabolism, the 

 characteristic inclusions appeared linked with a hitherto unrecognized type of 

 physiology, viz. the oxidation of an inorganic substance instead of the decomposition 

 of organic materials. From this oxidation the sulfur bacteria derive their energy 

 for maintenance and growth. 



* Completely revised by Prof. C. B. van Niel, Kopkins Marine Station, Pacific 

 Grove, California, January, 1944. 



