FAMILY II. ATHIORHODACEAE 



55 



1. Rhodopseudonionas palustris (Mo- 

 lisch, 1907) van Niel, 194-4. [Rhodobacillus 

 palustris ]Molisch, Rhodobacterium capsula- 

 tum Molisch and Rhodovibrio parvus Mo- 

 lisch, Die Purpurbakterien, Jena, 1907, 14, 

 18 and 21 ; van Niel, Bact. Rev., 8, 1944, 89.) 



pa.lu.s'tris. L. adj. paluster marshy, 

 swampy. 



Cells usually distinct!}^ rod-shaped, 

 though in young cultures very short, lightly 

 curved rods may often predominate. Size 

 variable, even for the same strain, and 

 strongly influenced by age of culture and 

 composition of medium. Rather consistently 

 short cells in young cultures in yeast ex- 

 tract, especially when incubated anaerobi- 

 cally in the light or in anaerobic cultures 

 with substrates, such as malonate, which 

 permit only a slow and scant develop- 

 ment. Dimensions in such cultures 0.6 to 0.8 

 by 1.2 to 2 microns. More often, especially 

 in older cultures, cells are much longer, up 

 to 10 microns. Highly characteristic is the 

 pronounced tendency to the formation of 

 irregularly shaped, bent and crooked long 

 rods, occasionally swollen at one or both 

 e.xtremities, and frequently suggesting 

 branching. Such cells usually form clusters 

 reminiscent of Corynebacterium and Myco- 

 bacterium cultures. 



Cells in young cultures actively motile by 

 means of polar flagella; irregular and long 

 cells as a rule non -motile. Gram-negative. 



Growth in liquid media never mucoid; 

 sediment in older cultures homogeneous and 

 smooth, readily redispersible. 



Color varies considerably, depending upon 

 the medium, and especially in anaero- 

 bic illuminated cultures. Where develop- 

 ment is slight (as in malonate, thiosulfate 

 and, usually, glycerol media), the color is a 

 light pink; in media containing fatty acids, 

 more nearly dark reddish brown. Color due 

 to bacteriochlorophyll and a number of dif- 

 ferent carotenoid pigments; most strains 

 produce, in addition, a water-soluble, non- 

 carotenoid, bluish red pigment which dif- 

 fuses into the culture medium. 



In yeast extract cultures growth is pos- 

 sible over the range pH 6 to 8.5. With cer- 

 tain substrates, especially fatty acids, the 

 combined effect of low pH and a substrate 

 concentration of 0.1 to 0.2 per cent may pre- 



vent growth. No characteristic odors save 

 that old cultures may develop a distinct 

 ionone-like fragrance. Gelatin is not lique- 

 fied; leucine is generally utilized as a sub- 

 strate. 



Most strains are able to grow on the sur- 

 face of agar plates or slants ; a few, especially 

 when first isolated, appear more sensitive to 

 oxygen and develop only in stabs in which 

 the upper region may remain free of growth. 

 Generally such strains can be adapted to 

 grow at full atmospheric oxygen tension. 



Most fatty acids and hydroxy acids are 

 adequate oxidation substrates. All cultures 

 can grow at the expense of thiosulfate and 

 produce rapid and profuse growth in glu- 

 tarate and ethanol media. No development 

 in media containing, as the chief oxidation 

 substrate, 0.2 per cent sorbitol, glucose or 

 mannose, even though these substances are 

 not inhibitory. Molecular hydrogen can be 

 oxidized. 



All cultures can develop anaerobically in 

 illuminated cultures by photosj^nthesis. 



p-amino-benzoic acid is required for 

 growth (Hutner). 



Optimum temperature generally rather 

 high, good development being possible up 

 to 37° C. However, certain strains exhibit a 

 lower optimum temperature. 



Distinctive characters : Morphological 

 resemblance to species of Mycobacterium in 

 old cultures, ability to grow with thiosulfate 

 as the chief oxidizable substrate, and failure 

 to develop in media which contain carbohy- 

 drates or sugar alcohols in a concentration 

 of 0.2 per cent as the main oxidizable com- 

 pounds. 



Habitat: Regularly found in mud and 

 stagnant bodies of water. 



Illustrations: Molisch, op. cit., 1907, 

 Plate I, fig. 1, 2; Plate II, fig. 10; van Niel, 

 op. cit., 1944, fig. 1-3, p. 18, and fig. 18-26, 

 p. 90. 



2. Rhodopseudomonas gelatinosa (Mo- 

 lisch, 1907) van Niel, 1944. (Rhodocystis 

 gelatinosa Molisch, Die Purpurbakterien, 

 Jena, 1907, 22; van Niel, Bact. Rev., 8, 1944, 



98.) 



ge.la.ti.no'sa. L. part. adj. gclatus frozen, 

 stiffened; M.L. gelatinum gelatin, that which 



