the form of irregular filaments. Outstandingly characteristic is the zigzag arrangement of the cells in chains. Gram-negative.
Cultures in media of pH 8 or above are distinctly mucoid.
Color: Anaerobic cultures develop with a brown color, the shade ranging from a light yellowish brown to a deep mahogany-brown. When grown in the presence of oxygen, the cultures are dark red. Even the pigmentation of the brown-colored organisms from an anaerobic culture can be changed into a distinct red by shaking a suspension with air for some hours; light enhances the rate of this color change. Color due to bacteriochlorophyll and carotenoid pigments. No diffusible water-soluble pigment is produced.
Growth possible over a pH range from at least 6 to 8.5, morphology becoming abnormal in the alkaline media.
Most cultures are odorless, although occasionally a faint peach-like odor can be detected.
Growth is not inhibited by the presence of oxygen, although the pigmentation is thereby affected.
Fatty acids and most substituted acids are satisfactory substrates. Rapid and abundant growth with propionate at a concentration of 0.2 per cent. At this same concentration glutaric acid leads, at best, to very meager cultures, while tartrate, citrate and gluconate fail to induce growth, as do also ethanol, glycerol, mannitol and sorbitol. In media with 0.2 per cent glucose or fructose good growth is obtained. No growth with mannose. Thiosulfate is not, but molecular hydrogen can be, oxidized by this species.
Gelatin is not liquefied; of the amino acids, alanine and glutamic acid are satisfactory substrates while leucine is not utilized.
Distinctive characters: Cell shape and arrangement in chains; brown color of anaerobic, red pigmentation of aerobic cultures; ability to grow in media with 0.2 per cent propionate, glucose, fructose, alanine and glutamic acid; failure to develop with leucine, as well as with ethanol, glycerol, mannitol and sorbitol in the above-mentioned concentration.
All cultures can develop anaerobically in illuminated cultures by a photosynthetic metabolism.
Thiamin is required for growth; a few strains require biotin and nicotinic acid in addition (Hutner).
Optimum temperature distinctly lower than for Rhodopseudomonas palustris, and, as a rule, around 25° C.
Habitat: Regularly found in stagnant bodies of water and in mud.
Illustrations: Molisch, op. cit., 1907, Plate II, fig. 9; van Niel, op. cit., 1944, fig. 4-6, p. 19; fig. 27-32, p. 92; and fig. 33-38, p. 93.
4. Rhodopseudomonas spheroides van Niel, 1944. (Rhodococcus capsulatus Molisch, Die Purpurbakterien, Jena, 1907, 20; Rhodococcus minor Molisch, ibid., 21; van Niel, Bact. Rev., 8, 1944, 95.)
sphe.ro.i′des or sphe.roi′des. Gr. adj. sphaeroides globular.
Cells generally single, nearly spherical, diameter without slime capsule variable, depending upon medium, ranging from 0.7 to 4 microns. In young cultures actively motile by means of polar flagella; motility soon ceases in media which are or become alkaline. Copious slime production in media at pH above 7. In strongly alkaline cultures abnormal cell-shapes occur in the form of irregular, swollen and distorted rods, often having the appearance of spore-bearing cells, simulated by the production of fat bodies. In sugar-containing media egg-shaped cells, measuring as a rule 2.0 to 2.5 by 2.5 to 3.5 microns, are frequently found. Gram-negative.
Color: Anaerobic cultures develop with brown color, ranging in shade from a light, dirty greenish brown to a dark brown. Cultures grown in the presence of oxygen are distinctly red. As in the case of Rhodopseudomonas capsulata, the brown color of an anaerobic culture can be changed to red by shaking with air, light stimulating the color change. Color due to bacteriochlorophyll and carotenoid pigments. The large majority of cultures of this species produce, in addition, a water-soluble, non-carotenoid, bluish red pigment which diffuses into the culture medium.
