FAMILY III. CHLOROBACTERIACEAE 61 



length varies in width from 4 to 6 microns glucose, hydrogen sulfide or thiosulfates. 



and in length from 7 to 10 microns; this is Strongly microaerophilic; tends to be 



dependent upon environmental conditions. strictly anaerobic, and hence capable of 



Actively motile by means of a single polar development only in illuminated cultures, 



flagellum. Does not liquefy gelatin. 



Color: Distinctly reddish brown due to Distinctive characters: Readily distin- 



the presence of bacteriochlorophyll and guishable from Rhodospirillum rubrum by 



carotenoids, the latter responsible for the the absence of an absorption band at 550 



absorption maxima at 520 and 485 milli- millimicrons and from R. fulvum and R. 



microns. Spirilloxanthin not formed. molischianum by the greater size of its cells. 



Capable of development under strictly Habitat: Stagnant water and mud; widely 



anaerobic conditions in media containing distributed. 



ethanol, fatty acids or hydroxy acids as Illustrations: Molisch, ibid., Plate 1, fig. 



oxidizable substrates. Citrate can also be 5-6; Giesberger, Jour. Microbiol, and Serol., 



utilized in this manner, but not glycerol, 13, 1947, fig. 6-9, p. 141. 



FAMILY III. CHLOROBACTERIACEAE LAUTERBORN, 1913. 



{Chlorobakteriaceae (sic) Lauterborn, Alg. Bot. Ztschr., 19, 1913, 99.) 



Chlo.ro. bac.te.ri.a'ce.ae. M.L. neut.n. Chlorobacterium type genus of the family; -aceae 

 ending to denote a family; M.L. fern. pi. n. Chlorobacteriaceae the Chlorobacterium family. 



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 de- 

 positing elemental sulfur outside the cells. Contain green pigments of a chlorophyllous 

 nature, though not identical with the common green plant chlorophylls nor with bacterio- 

 chlorophjdl. Capable of photosynthesis in the presence of hydrogen sulfide; do not liberate 

 oxygen. 



A number of genera have been proposed; some are characterized by special colonial growth 

 forms while others are characterized on the basis of a supposed symbiotic 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 Niel, Arch, f . Mikro- 

 hio\.,3, 1931, 65ff.), the validity of many of these genera is doubtful. The following 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. 62. 



B. Bacteria united into characteristic aggregates. 



1. Bacteria without intracellular sulfur globules. 



Genus II. Pelodictyon, p. 63. 



2. Bacteria with intracellular sulfur globules. 



Genus III. Clathrochloris, p. 64. 

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

 A. Aggregates composed of green bacteria and protozoa. 



Genus IV. Chlorobacterium, p. 65. 



