60 



ORDER I. PSEUDOMONADALES 



small size of the individual cells. These are 

 not over 0.5 micron wide and generally not 

 longer than 2.5 microns. The most common 

 shape consists of a complete turn of about 

 1 by 1.5 microns. In media with fatty acids 

 as a substrate the spirals appear somewhat 

 steeper than in fumarate, succinate or 

 malate cultures. Swollen individuals re- 

 sembling vibrios are encountered in cultures 

 which do not appear quite healthy. Forma- 

 tion of mucus or clumping has not been ob- 

 served. 



Gelatin is not liquefied; aspartate has been 

 the only amino acid capable of inducing 

 growth. Thiosulfate is not oxidized. 



Color: Quite distinct from that of Rhodo- 

 spirillum rubrimi; colonies and stab cul- 

 tures are a reddish brown while liquid cul- 

 tures often appear brownish orange. The 

 color is due to bacteriochlorophyll and 

 carotenoid pigments; among the latter 

 spirilloxanthin, as evidenced by the absence 

 of an absorption maximum at 550 milli- 

 microns, is not represented as a major con- 

 stituent. Does not produce water-soluble, 

 diffusible pigments. 



Capable of strictly anaerobic develop- 

 ment in illuminated cultures, due to photo- 

 synthetic metabolism. 



Fatty acids and the four-carbon dicar- 

 boxylic acids are imiformly good substrates; 

 glutarate is not used. Ethanol and glucose, 

 in a concentration of 0.2 per cent, have 

 yielded satisfactory cultures; other carbo- 

 hydrates, as well as the corresponding poly- 

 alcohols, have given negative results. 



Little information available concerning 

 pH and temperature relations. Behaves 

 generally as a strict anaerobe; adaptation 

 to microaerophilic conditions has not been 

 achieved. Negative aerotaxis very pro- 

 nounced. 



Distinctive characters : The small size and 

 the color of the cultures serve as adequate 

 criteria for its differentiation from Rhodo- 

 spirilhim ruhrum. The strictly anaerobic 

 nature and the failure to grow with glu- 

 tarate and various amino acids except as- 

 partate can probably be used as supple- 

 mentary specific properties. 



Habitat: Bodies of stagnant water and 

 mud . 



Illustrations: Van Niel, ibid., fig. 97-102, 



p. 109; Giesberger, Jour. Microb. and Serol., 

 13, 1947, fig. 1-2, p. 141. 



3. Rhodospirilluin niolischianuni 



Giesberger, 1947. (Jour. Microbiol, and 

 Serol., 13, 1947, 137.) 



mo.li.schi.an'um. M.L. adj. molischianus 

 pertaining to Molisch. 



Cells characteristically spiral -shaped, 

 moderately large, 0.7 to 0.9 by 5 to 10 mi- 

 crons. Mostly with one or two complete 

 turns which vary in width from 1.3 to 2 

 microns and in length from 4 to 6 microns; 

 this depends upon environmental condi- 

 tions. 



Color: Distinctly reddish brown due to 

 the presence of bacteriochlorophyll and 

 carotenoids, the latter responsible for the 

 absorption maxima at 520 and 485 milli- 

 microns. Spirilloxanthin absent. 



Capable of development under stricth^ 

 anaerobic conditions in media containing 

 ethanol or fatty- or hydroxy-acids as oxidiz- 

 able substrates. Citrate can also be utilized 

 in this manner, but not glycerol, glucose, 

 hydrogen sulfide or thiosulfates. Tends to be 

 strictl}^ anaerobic, and hence capable of 

 development onlj- in illuminated cultures. 



Does not liquefy gelatin. 



Distinctive characters : The absence of an 

 absorption band at 550 millimicrons and the 

 ability to utilize citrate serve to distinguish 

 this type from Rhodospirillum ruhrum, 

 which it closely resembles in size and shape. 

 The individual cell size differentiates this 

 species from R. fulvum and R. photometri- 

 cum. 



Habitat: Widely distributed. Regularly 

 present in stagnant water and mud; can be 

 found in abundance in anaerobic cultures of 

 hay extract inoculated with such materials 

 and incubated in light. 



Illustrations: Giesberger, ibid., fig. 3-5, 

 p. 141. 



4. Rhodospirillum photonietricum 



Molisch, 1907. (Die Purpurbakterien, Jena, 

 1907, 24.) 



pho.to.me'tri.cum. Gr. noun phos light; 

 Gr. adj. metricus measured; M.L. adj. 

 photometriciis light-measured. 



Cells large, stout, spiral -shaped. Mostly 

 with one or two complete turns whose wave 



