length varies in width from 4 to 6 microns and in length from 7 to 10 microns; this is dependent upon environmental conditions. Actively motile by means of a single polar flagellum.
Color: Distinctly reddish brown due to the presence of bacteriochlorophyll and carotenoids, the latter responsible for the absorption maxima at 520 and 485 milli microns. Spirilloxanthin not formed.
Capable of development under strictly anaerobic conditions in media containing ethanol, fatty acids or hydroxy acids as oxidizable substrates. Citrate can also be utilized in this manner, but not glycerol, glucose, hydrogen sulfide or thiosulfates. Strongly microaerophilic; tends to be strictly anaerobic, and hence capable of development only in illuminated cultures.
Does not liquefy gelatin.
Distinctive characters: Readily distinguishable from Rhodospirillum rubrum by the absence of an absorption band at 550 millimicrons and from R. fulvum and R. molischianum by the greater size of its cells.
Habitat: Stagnant water and mud; widely distributed.
Illustrations: Molisch, ibid., Plate 1, fig. 5-6; Giesberger, Jour. Microbiol, and Serol., 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. pl. 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 depositing elemental sulfur outside the cells. Contain green pigments of a chlorophyllous nature, though not identical with the common green plant chlorophylls nor with bacteriochlorophyll. 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 microorganisms. 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 . Mikrobiol., 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.
