56 



ORDER I. PSEUDOMONADALES 



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 mi- 

 crons, 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 cul- 

 tures of Rhodopseudomonas palustris, but 

 the characteristic Mycobacterium-Yike clus- 

 ters of the latter are absent. Single cells in- 

 frequent due to a copious mucus produc- 

 tion in all media which causes the cells to 

 clump together. While young cells are ac- 

 tively motile by means of polar flagella, 

 motility is often difficult to ascertain as a 

 result of the pronounced tendency to con- 

 glomerate; 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 sub- 

 strates. 



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 ex- 

 tract (when a much heavier growth is ob- 

 tained than with low concentrations supple- 

 mented 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 j^east 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 man- 

 nose, 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 in- 

 cubated slants or agar plates. 



Capable of strictly anaerobic development 

 in illuminated cultures by virtue of a photo- 

 synthetic 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 gela- 

 tin, 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 (Mo- 

 lisch, 1907) van Niel, 1944. {Rhodonostoc 

 capsulatum Molisch, Die Purpurbakterien, 

 Jena, 1907, 23; Rhodopseudomonas capsulatus 

 (sic) van Niel, Pact. Rev., S, 1944, 92.) 



cap.su.la'ta. L. dim. noun capsula a small 

 chest, capsule; M.L. adj. capsulatus capsu- 

 lated. 



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; thej' are 

 usually arranged in chains resembling strep- 

 tococci. 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 mi- 

 crons. At pH above 8, abnormal growth in 



