FAMILY CHLOROBACTERIACEAE 869 



FAIVIILY III. CHLOROBACTERIACEAE GEITLER AND PASCHER.* 



(Cyanochloridinae-Chlorobacteriaceae Geitler and Pascher, Die Siisswasserflora 

 Deutschlands, Osterreichs und der Schweiz, Jena, 12, 1925, 451; Chlorothiobacteria 

 Bavendamm, Ergeb. Biol., 13, 1936, 49.) 



Green bacteria, usually of small size, occurring singly or in cell masses of various 

 shapes and sizes, developing in environments containing rather high concentrations 

 of hydrogen sulfide and exposed to light. As a rule not containing sulfur globules 

 but frequently depositing elementary sulfur outside the cells. Contain green pig- 

 ments of a chlorophyllous nature, though not identical with the common green plant 

 chlorophylls nor with bacteriochlorophyll. Capable of photosynthesis in the pres- 

 ence of hydrogen sulfide; do not liberate oxygen. 



A number of genera have been proposed, characterized by special colonial growth 

 forms, others on the basis of a supposed s3-mbiotic habitus, where the green bacteria 

 grow in more or less characteristic aggregates together with other micro-organisms. 

 In view of the variations in size and shape exhibited by the only member of this 

 group which has so far been obtained and studied in pure culture (van Xiel, Arch. f. 

 Mikrobiol., 3, 1931, 65fT.) the validity of many of these genera is doubtful. The fol- 

 lowing keys and descriptions, therefore, bear a strictly provisional character. Here, 

 as in the case of the sulfur purple bacteria, significant advances can only be expected 

 from pure culture studies under controlled environmental conditions. 



Key to the genera of family Chlorobacteriaceae. 



I. Free-living bacteria not intimately associated with other microbes, 

 a. Bacteria not united into well defined colonies. 



Genus I. Chlorobium, p. 869. 

 aa. Bacteria united into characteristic aggregates. 



b. Bacteria without intracellular sulfur globules. 



Genus II. Pelodictyon, p. 870. 

 bb. Bacteria with intracellular sulfur globules. 



Genus III. Clathrochloris, p. 872. 

 II. Green bacteria found as symbiotic aggregates with other organisms, 

 a. Aggregates composed of green bacteria and protozoa. 



Genus IV. Chlorobacteriuin, p. 872. 

 aa. Aggregates composed of two different types of bacteria. 



b. Aggregates small, barrel-shaped, actively motile, and consisting of a 

 central, polarly flagellated, rod-shaped bacterium with a covering of 

 green sulfur bacteria. 



Genus V. Chlorochromatium, p. 873. 

 bb. Aggregates large, cylindrical, non-motile, and composed of a central 

 filamentous bacterium with a more or less extensive covering of green 

 sulfur bacteria. 



Genus VI. Cylindrugloea, p. 873. 



Genus I. Chlorobium Nadson. 



(Xadson, Bull. Jard. Imper. Botan., St. Petersb., 12, 1912, 64 (Russian), 83 (Ger- 

 man) ; Chloronostoc Pascher, Die Siisswasserflora Deutschlands, Osterreichs und der 

 Schweiz, Jena, 12, 1925, 456; Tetrachloris Pascher, ibid., 455; Sorochloris? Pascher, 



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

 Grove, California, January, 1944. 



