58 



ORDER I. PSEUDOMONADALES 



Gelatin is not liquefied, and growth with 

 single amino acids appears somewhat er- 

 ratic. 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 Rhodopseudo- 

 7nonas palustris or Rhodopseudomonas capsu- 

 lata 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, fruc- 

 tose and mannose in 0.2 per cent concentra- 

 tions. 



In sugar-containing media, acid is pro- 

 duced; the pH ma}^ 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 ex- 

 posed 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 anaero- 

 bic and red pigmentation of aerobic cul- 

 tures; growth with 0.2 per cent tartrate, 

 gluconate, ethanol, glycerol, mannitol, 

 sorbitol, glucose, fructose and mannose; 

 failure to grow with 0.2 per cent propio- 

 nate. 



Habitat: Regularly found in stagnant 

 bodies of water and in mud. 



Illustrations : INIolisch, 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. 



Genvs 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 Phaeospirilhtm 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 bac- 

 teriochlorophyll and are potentially photosynthetic in the presence of extraneous oxi- 

 dizable 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, espe- 

 cially 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 ruhrum. 



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 Julvum. 



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. 



