856 MANUAL OF DETERMINATIVE BACTERIOLOGY 



taining hydrogen sulfide and exposed to Illustrations: ^vlolisch, Die Purpur- 



light. Not reported from sulfur springs. bakterien, Jena, 1907, PI. II, fig. 13-14. 



Genus XIII. Chromatium Perty. 



(Perty, Zur Kenntniss kleinster Lebensformen, Bern, 1852, 174; Rhodomonas Orla- 

 Jensen, Cent. f. Bakt., II Abt., 22, 1909, 334.) From Greek chroma, color. 



Cells occur singly, more or less ovoid, bean- or vibrio-shaped, or short rods. The 

 last-mentioned are often thick-cylindrical with rounded ends. Motile by means of 

 polar flagella. Contain bacteriochlorophyll and carotenoid pigments, coloring the 

 cells various shades of red. Capable of photosynthesis in the presence of hydrogen 

 sulfide and storing elementary sulfur as an incomplete oxidation product in the form 

 of globules inside the cells. 



At present, the genus contains 11 described species and one variety'. In addition, 

 two more purple sulfur bacteria, Pscudomonas molischii Bersa (Planta, 2, 1926, 375) 

 and Thiospir ilium cocci neiim Hama (Jour. Sci. Hiroshima Univ., Ser. B, Div. 2, 

 Bot., 1, 1933, 158), have been incorporated here as species of Chromatium because 

 the descriptions and illustrations furnished by the original authors leave no doubt 

 as to their taxonomic affiliations. 



Differentiation of species has, in the past, been based almost entirely upon size 

 and shape of individual cells, often with complete disregard for the variability of 

 these criteria. The unsatisfactory and arbitrary nature of such a classification has 

 occasionally been pointed out, and with much justification. Winogradsky (Schwef- 

 elbacterien, Leipzig, 1888, 98) mentions the many transitional stages that can be 

 observed between Chromatium okenii and Chromatium. weissei; Strzeszewski (Bullet. 

 Acad. Sci., Cracovie, S^r. B, 1913, 321) holds that it is impossible to distinguish, on 

 the basis of sizes or otherwise, between Chromatium veissei and Chromatium minus. 

 Such contentions, derived from observations on material from natural collections or 

 crude cultures, have been greatly strengthened by studies with pure cultures of 

 species of Chromatium. Thus van Niel (Arch. f. Mikrobiol., 3, 1931, 59) reported 

 variations in width from 1 to 4 microns, and in length from 2 to 10 microns or even 

 up to 50 microns; Manten (Antonie van Leeuwenhoek, 8, 1942, 164 ff.) found size 

 differences of 1 to 14 microns with a pure culture of an organism that he identified as 

 Chromatium okenii. Often the differences in size of a pure culture can be related to 

 special environmental conditions. On account of such results a designation of species 

 on the basis of size relations alone is manifestly unsatisfactory. Moreover, the 

 available data do not suggest that differences in shape, color or arrangement of sulfur 

 globules can be used more effectively. Lack of adequate experimental results with 

 a sufficiently large number and variety of pure cultures prevents a more rational 

 classification at present. 



The previously proposed species have been listed below with their respective 

 characteristics and arranged as far as possible in the order of decreasing width. 



Two Chromatium species have been described as containing inclusions of calcium 

 carbonate in addition to sulfur globules. .Vs in the case of Rhabdomonas linsbaueri, 

 it is not known whether this feature may be a direct consequence of the calcium ion 

 content and pH of the environment, and thus fail to have taxonomic significance. 



The type species is Chromatium okenii Perty. 



1. Chromatium gobii Issatchenko. glacial arcticiue, Petrograd, 1914^ 253.) 

 (Recherchos sur los microbes do Tocean Xainoii for Prof. X. TJobi. 



