840 MANUAL OF DETERMINATIVE BACTERIOLOGY 



Certain genera of sulfur purple bacteria, created by Winogradsky, will verj' prob- 

 ably be consolidated when detailed information concerning the morphology of the 

 organisms is available. Until such time it seems, however, best to retain most of 

 them, even though the distinguishing characteristics are not always very clear. For 

 the benefit of those who are familiar with previous methods of classification it will 

 be indicated where deviations have been adopted. 



The non-sulfur purple bacteria {Athiorhodaceae Molisch; Rhodobacterioideae 

 Buchanan) have been subjected to a comparative morphological and physiological 

 study comprising more than 150 strains, among which all previously proposed genera 

 and species are represented (Van Xiel, Bact. Rev., 8, 1944, 1-118). It has been found 

 that the characteristics upon which Molisch based the seven genera of this group are 

 inadequate, and a new classification with only two distinguishable genera has been 

 proposed. This system will be followed here. 



Nadson (Bull. Jard. Imper. Bot., St. Petersburg, 12, 1912, 64) described a new type 

 of small, green bacteria, not containing sulfur globules in the presence of hydrogen 

 sulfide, but e.xcreting elementary sulfur. These appear incapable of oxidizing sulfur 

 compounds other than sulfides. They are photosynthetic and are capable of growing 

 in anaerobic culture when illuminated. The green pigment differs from the green 

 plant chlorophylls and from the bacteriochlorophyll of the purple bacteria, but has 

 the characteristics of a chlorophyllous compound. These are grouped in the family 

 Chlorobacteriaceae. 



