FAMILY THIORHODACEAE 



851 



tions with material from natural collections and from laboratory mass cultures. The 

 criteria used are the size and shape of the spirals, and the color of the organisms. 

 Not a single representative has so far been obtained and studied in pure culture, so 

 that no information is available concerning the constancy or variability of these 

 characteristics. It is, however, likely that such properties may be greatly influ- 

 enced by environmental factors. Hence, the following key and descriptions of 

 species are apt to be modified when more extensive studies have been made. The 

 published descriptions of some species make it seem probable that they should not 

 even be incorporated in Thiospirillum. 



The type species is Thiospirillum jenense (Ehrenberg) Winogradsky. 



Key to the species of genus Thiospirillum. 



I. Width of cells 2.5 microns or more. 



1. Color of cells, especially in masses, yellowish-brown to orange-brown. 



1. Thiospirillum jenense. 



2. Color of cells deep red or violet. 



a. Cells long, typical spirals; clearly red. 



2. Thiospirillum sanguineum. 



aa. Cells short, slightly curved, vibrio-shaped; color purple to violet-red. 



3. Thiospirillum violaceum. 

 II. Width of cells less than 2.5 microns. 



1. W^idth of cells 1.5 to 2.5 microns. 



4. Thiospirillum rosenhergii. 



2. Width of cells about 1 micron. 



5. Thiospirillum rufum. 



1. Thiospirillum jenense (Ehrenberg) 

 Winogradsky. {Ophidomonas jenensis 

 Ehrenberg, Die Infusionstierchen, 

 Leipzig, 1838, 44; Spirillum jenense 

 Trevisan, Batter, ital., 1879, 26; Wino- 

 gradsky, Schwefelbacterien, Leipzig. 

 1888, 104; Rhodothiospir ilium jenense 

 Ellis, Sulphur Bacteria, London and 

 New York, 1932, 161; Thiospirillum 

 crassum Hama, Jour. Sci. Hiroshima 

 Univ., Ser. B, Div. 2, Bot., 1, 1933, 157.) 

 Named for the city of Jena, Germany, 

 where Ehrenberg discovered this or- 

 ganism. 



Cells: Cylindrical, sometimes pointed 

 at ends, 2.5 to 4 microns long, coiled as 

 spirals. Generally 30 to 40 microns in 

 length but may be as long as 100 microns. 

 Shape of individual coils varies, complete 

 turns measuring about 15 to 40 microns 

 in length, and from | to 1/10 of the width 

 in height. Polar flagellate. Tufted at 

 both ends. Olive-brown, sepia-brown 

 and reddish-brown. 



This coloring appears to be the only 

 recognizable difference from Thiospiril- 

 lum sanguineum . Thiospirillum cras- 

 sum Hama {loc. cit.) reported to be 3.7 

 to 4 by 12 to 40 microns and yellowish- 

 brown in color, thus becomes indis- 

 tinguishable from Thiospirillum jenense; 

 the 80 microns long Thiospirillum je- 

 nense forma maxima Szafer (Bull. Acad. 

 Sci. Cracovie, Ser. B, 1910, 162) does not 

 at present justify recognition as a special 

 taxonomic entity. 



It is even doubtful whether the ob- 

 served color difference between Thio- 

 spirillum jenense and Thiospirillum 

 sanguineum constitutes a valid criterion 

 for their maintenance as two distinct 

 species (Buder, Jahrb. wiss. Bot., 56, 

 1915, 534; Bavendamm, Die farblosen 

 und roten Schwefelbakterien, Pflanzen- 

 forschung. Heft 2, 1924, 131). 



Habitat: Mud and stagnant water con- 

 taining hydrogen sulfide and exposed to 

 light; more rarely in sulfur springs. 



