stiffens; M.L. adj. gelatinosus full of gelatin, gelatinous.
Cells in young cultures short and small rods, approximately 0.5 by 1 to 2 microns. In old cultures much longer, up to 15 microns, and then irregularly curved rods, often swollen and gnarled in places up to 1 micron in width. In this stage the cells bear some resemblance to those found in old cultures of Rhodopseudomonas palustris, but the characteristic Mycobacterium-like clusters of the latter are absent. Single cells infrequent due to a copious mucus production in all media which causes the cells to clump together. While young cells are actively motile by means of polar flagella, motility is often difficult to ascertain as a result of the pronounced tendency to conglomerate; the individuals in the clumps appear to be non-motile. Gram-negative. Gelatin is liquefied; of the single amino acids alanine, asparagine, aspartic and glutamic acids appear generally satisfactory substrates.
Color quite distinctive in most anaerobic cultures as a pale, delicate, pinkish shade, rather peach-colored. Only in the presence of rather high concentrations of yeast extract (when a much heavier growth is obtained than with low concentrations supplemented with 0.2 per cent of various single oxidation substrates) do the slimy cell masses appear a dirty, faded brown. Color is due to bacteriochlorophyll and carotenoid pigments. Occasionally a water-soluble, non-carotenoid, bluish red pigment is produced which diffuses into the culture medium.
In yeast extract, growth occurs over a pH range extending from at least 6.0 to 8.5.
Cultures produce a characteristic acrid odor.
More sensitive to fatty acids than are other species of Rhodopseudomonas; with 0.2 per cent propionate no growth occurs. The best single oxidizable substrates appear to be ethanol, glucose, fructose and mannose, as well as a variety of amino acids. Citrate also permits good growth; not, on the other hand, glycerol, mannitol, sorbitol or tartrate in the usual concentration of 0.2 per cent.
Thiosulfate is not oxidized; behavior towards molecular hydrogen unknown.
More pronouncedly microaerophilic than the other Rhodopseudomonas species; most cultures cannot develop on aerobically incubated slants or agar plates.
Capable of strictly anaerobic development in illuminated cultures by virtue of a photosynthetic metabolism.
Thiamin plus biotin is required for growth (Hutner).
Temperature relations so far unknown.
Distinctive characters: The small size of the individual cells and the pronounced clumping which causes the cultures to be exceptionally stringy; the unusual color of the cell masses; the ability to liquefy gelatin, to utilize citrate and a number of amino acids. Correlated with these is the failure to grow in media with 0.2 per cent propionate, tartrate and glycerol.
Habitat: Regularly present in stagnant bodies of water and in mud.
Illustrations: Molisch, op. cit., 1907, Plate I, fig. 8; van Niel, op. cit., 1944, fig. 55-60, p. 99; fig. 61-66, p. 100.
3. Rhodopseudomonas capsulata (Molisch, 1907) van Niel, 1944. (Rhodonostoc capsulatum Molisch, Die Purpurbakterien, Jena, 1907, 23; Rhodopseudomonas capsulatus (sic) van Niel, Pact. Rev., 8, 1944, 92.)
cap.su.la'ta. L. dim. noun capsula a small chest, capsule; M.L. adj. capsulatus capsulated.
Depending upon the pH of the medium, cells nearly spherical, or as distinct rods, often devoid of motility. Motility due to polar flagella. The spherical cells are found in media with a pH below 7; they are usually arranged in chains resembling streptococci. Rod-shaped cells are characteristic for media with pH above 7; the higher the pH, the longer the rods. Individual cells slightly less than 1 micron wide, although attenuated rods (about 0.5 micron in width) are frequent at pH above 8, and slightly swollen cells (to 1.2 microns) are found in media containing sugars. Length varies from 1 to 6 microns; most common dimensions in approximately neutral media, 2 to 2.5 microns. At pH above 8, abnormal growth in
