Gelatin is not liquefied, and growth with single amino acids appears somewhat erratic. No definite correlations have been observed.
Development is possible over a wide pH range, extending from at least 6.0 to 8.5.
All cultures exhibit an unpleasant putrid odor.
Requires for optimal development higher concentrations of yeast extract as a supply of growth factors than either Rhodopseudomonas palustris or Rhodopseudomonas capsulata and is more sensitive to low fatty acid concentrations. With 0.2 per cent propionate in a neutral medium, no growth occurs; caproic and pelargonic acids are toxic in concentrations below 0.1 per cent. On the other hand, tartrate and gluconate can serve as oxidation substrates, as can also ethanol, glycerol, mannitol, sorbitol, glucose, fructose and mannose in 0.2 per cent concentrations.
In sugar-containing media, acid is produced; the pH may drop to below 4.0 before development ceases. Acid production from glucose occurs both in presence and absence of air, and in illuminated as well as in non-illuminated cultures. In cultures exposed to light, the acid usually disappears later on.
Thiosulfate is not oxidized; hydrogen oxidation has not been observed.
Oxygen does not prevent growth; colonies develop on the surface of agar plates exposed to air, with a red pigmentation. Capable of strictly anaerobic development in illuminated cultures by photosynthesis.
Thiamin, biotin and nicotinic acid are required for growth (Hutner).
Optimum temperature, below 30° C.
Distinctive characters: Spherical cell-shape in most media; brown color of anaerobic and red pigmentation of aerobic cultures; growth with 0.2 per cent tartrate, gluconate, ethanol, glycerol, mannitol, sorbitol, glucose, fructose and mannose; failure to grow with 0.2 per cent propionate.
Habitat: Regularly found in stagnant bodies of water and in mud.
Illustrations : Molisch, op. cit., 1907, Plate II, fig. 15; van Niel, op. cit., 1944, fig. 7-8, p. 19; fig. 39-45, p. 96; fig. 46-54, p. 97.
Genus II. Rhodospirillum Molisch, 1907, emend, van Niel, 1944.
(Molisch, Die Purpurbakterien, Jena, 1907, 24; van Niel, Bact. Rev., 8, 1944, 86; the genus now includes the genus Phaeospirillum Kluyver and van Niel, Zent. f. Bakt., II Abt., 94, 1936, 396.)
Rho.do.spi.ril′lum. Gr. noun rhodum the rose; Gr. noun spira a coil, a spiral; M.L. dim. neut. n. Spirillum a bacterial genus; M.L. neut.n. Rhodospirillum the rose Spirillum.
Spiral-shaped bacteria, motile by means of polar flagella. Gram-negative. Contain bacteriochlorophyll and are potentially photosynthetic in the presence of extraneous oxidizable substances. Molecular oxygen is not produced. Unable to grow in strictly mineral media, even when possessed of the ability to utilize hydrogen as oxidizable substrate, due to the need for organic nutrilites. Produce accessory pigments causing the cultures, especially when grown in the light, to appear in various shades of red to brown.
The type species is Rhodospirillum rubrum (Esmarch) Molisch.
Key to the species of genus Rhodospirillum.
I. Cultures deep red without brownish tinge; characteristic absorption band around 550 millimicrons.
1. Rhodospirillum rubrum.
II. Cultures reddish brown to orange; characteristic absorption maximum around 520, not 550, millimicrons.
- A. Cells 0.5 or less micron in width.
2. Rhodospirillum fulvum.
- B. Cells more than 0.5 micron wide.
- 1. Size of cells 0.7 to 0.9 by 5 to 10 microns.
3. Rhodospirillum molischianum.
- 2. Size 1.2 to 1.5 by 14 to 30 microns.
4. Rhodospirillum photometricum.
