FAMILY ATHIORHODACEAE 



867 



Contain bacteriochlorophyll and are potentially photosynthetic in the presence of 

 extraneous oxidizable 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, especially 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 red; cells well over 0.5 micron, usually about 1 to 1.2 microns in width. 



1. Rhodospirillum rubrum. 

 II. Cultures brown to orange; cells 0.5 micron or less in width. 



2. Rhodospirillum fulvum. 



1. Rhodospirillum rubrum (Esmarch) 

 Molisch. [Spirillutn rubrum p]smarch. 

 Cent. f. Bakt., 1, 1887, 225; Molisch, Die 

 Purpurbakterien, Jena, 1907, 25; Rhodo- 

 spirillum. photometricum Molisch, ibid., 

 24; Rhodospirillum giganteum Molisch, 

 ibid., 24; Rhodospirillum longum Hama, 

 Jour. Sci. Hiroshima Univ., Ser. B, Div. 

 2, 1, 1933, 135; Rhodospirillum gracilc 

 Hama, ibid., 159.) From Latin ruber, 

 red. 



Cells: Characteristically spiral- 

 shaped, but size of elements variable 

 within wide limits, depending upon en- 

 vironmental conditions during growth. 

 Width of cells from 0.5 to 1.5 microns; 

 length from 2 to 50 microns, and over; 

 even in a single culture such differences 

 may be found. Also the shape and size 

 of the spiral coil varies much; it usually 

 ranges between 1 to 4 microns in width, 

 and from 1.5 to 7 microns in length. In 

 alanine media the majority of the cells 

 occurs in the form of half-circles to com- 

 plete rings; malate media tend to pro- 

 duce much flattened spirals. 



In old cultures involution forms ap- 

 pear, straightened spirals and irregularly 

 swollen cells, the latter common in 

 media with higher fatty acids. Such 

 cells stain irregularly, contain fatty in- 

 clusions, and are occasionally branched. 



Mucus is not produced. In calcium- 

 delicient media the growth is flocculent, 

 as if agglutinated. With an adequate 

 calcium supply the growth in liquid 



media is homogeneous, suspended, and 

 consists of single cells. 



Young cultures show active motility, 

 due to polar flagella. Gram-negative. 



Gelatin is not liquefied; the amino 

 acids alanine, asparagine, aspartic and 

 glutamic acids are satisfactory oxidiz- 

 able compounds. 



Color: Ordinarily deep and dark red, 

 without any brownish tinge. In ethanol 

 media lighter, and a characteristic pink. 

 Pigment production markedly influenced 

 by oxygen and light. Slants incubated 

 in darkness present a pale grayish sur- 

 face growth with a faint reddish hue, 

 while often showing deep-red cell masses 

 in the region between glass wall and agar 

 surface where development proceeds at 

 low oxygen tension. The color is due to 

 bacteriochlorophyll and carotenoid pig- 

 ments. Among the latter spirilloxan- 

 thin is quantitatively predominant. 

 Water-soluble, diffusible pigments are 

 not produced. 



Development possible over a pH range 

 of at least 6 to 8.5, although, as in other 

 cases, the combination of an acid reac- 

 tion and the presence of fatty acids may 

 prevent growth. 



Cultures produce a distinctive odor, 

 reminiscent of slightly putrid yeast. 



In general, grow well with fatty acids 

 as the chief oxidizable substrate; how- 

 ever, are prevented from growing by 

 0.2 per cent propionate in a neutral 

 medium. Most substituted acids are 

 equally satisfactory, with the exception 



