460 APPENDIX 



As the names indicate, the Chlorobacteriaceae are green, while 

 the Thio- and Athiorhodaceae appear in various shades of purple, 

 red, and brown. All of the photosynthetic bacteria contain chlorophyll- 

 ous as well as carotenoid pigments, and the differences in color of 

 cultures of various types are mainly attributable to variations in the 

 nature and proportions of the carotenoid components. Besides, the 

 color may be influenced by environmental conditions. For example, 

 cultures of green and purple sulfur bacteria growing in the presence 

 of H2S are usually opaque and pastel-colored, due to the presence of 

 highly refractile sulfur globules. In the Thiorhodaceae these globules 

 are found within the cells, in the much smaller Chlorobacteriaceae, 

 outside. After the H2S supply has been depleted and the sulfur further 

 oxidized to sulfate, the cultures become more transparent, and the 

 color changes to a deeper hue. 



The chlorophyll of the green sulfur bacteria has been designated 

 as "chlorobium chlorophyll." It accounts for the strong i';; vivo absorp- 

 tion in the near infrared region, around 750 m/;. The pigment can be 

 extracted from these bacteria by organic solvents, such as methanol, 

 ethanol, acetone, and diethyl ether; but such solutions do not exhibit 

 the marked infrared absorption band. The maximum is shifted towards 

 shorter wavelengths, and the in vitro absorption spectra of extracts 

 from various strains of Chlorobium have revealed that there exist at 

 least two different chlorobium chlorophylls (1). Furthermore, the re- 

 cent studies of Olson and Romano (2) and of Sybesma and Olson (3) 

 have shown that both Chlorobium and Chloropseudomonas also contain 

 a chlorophyll that is spectroscopically indistinguishable from the major 

 chlorophyllous component of the Thio- and Athiorhodaceae: bacterio- 

 chlorophyll a (see below). 



The green pigment of the Thio- and Athiorhodaceae, designated as 

 bacteriochlorophyll, has long been considered to represent a single 

 entity, even though the in vivo absorption spectrum of various purple 

 bacteria may show clear-cut differences. The absorption maxima in the 

 infrared region are situated between 800 and 900 m/y. But some 

 species exhibit up to three well-defined maxima, usually at 800, 850, 

 and 890 m/y, while in others only one absorption peak, at 870 m/i, may 

 be evident. Nevertheless, the in vitro absorption spectra of the bac- 

 teriochlorophyll extracted from different strains— which is shifted 

 toward the shorter wavelength side, as in the case of chlorobium 

 chlorophyll, and corresponds to about 770 m/y— has often been reported 

 as identical; and this holds equally for the absorption spectra of the 

 pheophytin solutions prepared by treatment of bacteriochlorophyll with 

 acid. These observations have been interpreted to mean that the in 

 vivo differences should be attributed (a) to the presence of a single 

 bacteriochlorophyll which, in the native state, can be bound to different 

 proteins; and (b) to a close spatial association of the green pigment 

 with other substances, in particular with carotenoids (4,5). However, 



