FAMILY II. ATHIORHODACEAE 



59 



1. Rhotlospirillum rubruni (von Es- 

 march, 1887) Molisch, 1907. {Spirillum rub- 

 rum von Esmarch, Cent. f. Bakt., 1, 1887, 

 225; Rhodospirillum giganteum Molisch, Die 

 Purpurbakterien, Jena, 1907, 24; Molisch, 

 ibid., 25.) 



rub'rum. L. adj. ruber red. 



Cells characteristically spiral-shaped, but 

 size of elements variable within wide 

 limits, depending upon environmental con- 

 ditions during growth. Width of cells from 

 0.5 to 1.5 microns; length from 2 to 50 mi- 

 crons, 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 occur in the 

 form of half -circles to complete rings; 

 malate media tend to produce much flat- 

 tened spirals. In old cultures involution 

 forms appear, straightened spirals and ir- 

 regularly swollen cells, the latter common in 

 media with higher fatty acids. Such cells 

 stain irregularly, contain fatty inclusions, 

 and are occasionally branched. Young cul- 

 tures show active motility, due to polar 

 fiagella. Gram-negative. 



Mucus is not produced. In calcium-defi- 

 cient media the growth is flocculent, as if 

 agglutinated. With an adequate calcium 

 supply the growth in liquid media is ho- 

 mogeneous, suspended and consists of single 

 cells. 



Gelatin is not liquefied; the amino acids 

 alanine, asparagine, aspartic and glutamic 

 acids are satisfactory oxidizable 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 dark- 

 ness present a pale grayish surface growth 

 with a faint reddish hue, while often show- 

 ing deep-red cell masses in the region 

 between glass wall and agar surface where 

 development proceeds at low oxygen ten- 

 sion. The color is due to bacteriochlorophyll 

 and carotenoid pigments. Among the latter, 

 spirilloxanthin is quantitatively predomi- 

 nant and is responsible for the characteristic 

 absorption band at 550 millimicrons. Water- 

 soluble, diffusible pigments are not pro- 

 duced. 



Development possible over a pH range of 

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

 the combination of an acid reaction 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; however, are 

 prevented from growing by 0.2 per cent 

 propionate in a neutral medium. Most sub- 

 stituted acids are equally satisfactory, with 

 the exception of tartrate, gluconate and 

 citrate. In a concentration of 0.2 per cent, 

 ethanol is a suitable substrate, whereas 

 the carbohydrates and their corresponding 

 polyalcohols are not utilized. 



Thiosulfate is not oxidized; molecular hy- 

 drogen can be used by some strains. 



Rather microaerophilic; many strains, 

 upon initial isolation, incapable of growth 

 at atmospheric oxygen tension. Subse- 

 quent adaptation can be induced, but even 

 such adapted cultures exhibit negative 

 chemota.xis to air. 



Capable of strictly anaerobic develop- 

 ment in illuminated cultures on the basis 

 of a photosynthetic metabolism. 



Biotin is required for growth (Hutner). 



Optimum temperature generally between 

 30° and 37° C. 



Distinctive characters: The most im- 

 portant characteristics of the species are 

 the spiral shape, combined with the ability 

 to produce a red pigment with a definite 

 absorption maximum at 550 millimicrons 

 in the intact cells. Diagnostically useful are 

 the good growth in media with 0.2 per cent 

 ethanol, alanine, asparagine, aspartate or 

 glutamate and the inadequacy of similar 

 concentrations of carbohydrates and thio- 

 sulfate as substrates. 



Habitat: Regularly present in stagnant 

 bodies of water and in mud. 



Illustrations: Molisch, ibid., Plate I, fig. 

 5-7; van Niel, Bact. Rev., 8, 1944, fig. 9-10, 

 p. 19; fig. 11-16, p. 24; fig. 67-75, p. 103; fig. 

 76-84, p. 104; fig. 85-90, p. 106; fig. 91-96, p. 

 107. 



2. Rhodospirillum fulvum van Niel, 

 1944. (Bact. Rev., 8, 1944, 108.) 



ful'vum. L. adj. fulvus deep or reddish 

 j^ellow, tawn3^ 



Characteristic for the species is the very 



