SPECTRA OF PHOTOSYNTHETIC PIGMENTS 373 



of combination are present even in a single species of these bacteria, thus 

 causing the absorption peaks to occur in various positions. 



Katz and Wassink (1939) have also investigated aqueous extracts of 

 photosynthetic bacteria containing the pigments in a water-soluble form 

 combined, presumably, with protein. These aqueous extracts, prepared 

 either by grinding or by the use of supersonic vibration, can be clarified 

 by the addition of urea and probably also other detergents without shift 

 of the band position from that of the live cells. The absorption spectra 

 of several such preparations from different species are shown in Fig. G-12 

 (French, 1940a). These measurements were made in a spectrophotome- 

 ter in which the photocell was placed very close to the solution; this 

 further reduced the likelihood of distortion by light scattering. These 

 curves also show large variations in relative height of the 790- and the 

 850-m|i absorption bands and perhaps small variation in position. In 

 the Phacomonas curve the infrared band shows a pronounced shoulder 

 at about 870 m/x. Alore data for the absorption spectra of the bacterial 

 extract and of the intact bacteria are shown in Figs. 6-13 and 15. The 

 infrared part of the absorption spectrum of these bacteria on a frequency 

 plot has been analyzed as sums of three to five symmetrical components 

 by Wassink et al. (1939). Variations in the relative proportions of these 

 different bands lead to the wide variation in the shape of the bacterial- 

 absorption curves. Between 420 and 550 m/z a large part of the absorp- 

 tion of these bacteria is due to the presence of carotenoid pigments. 

 Comparisons of the absorption in this region in Figs. 6-12 through 15 

 show that the nature of the carotenoids in different species varies greatly. 



In Fig. 6-14 the absorption curves of some of the isolated purple bacteria 

 carotenoids in benzene solution are shown. The best known of these is 

 spirilloxanthin, studied by Van Niel and Smith (1935) and by Polgar 

 ct al. (1944), which occurs in Rhodospirillum ruhrum. Parts c, d, and e 

 of Fig. 6-14 show the other carotenoids isolated chromatographically by 

 Manten (1948) from R hod o spirillum ruhrum. These pigments are pres- 

 ent in far smaller quantities than spirilloxanthin is, but it is evident 

 from the action spectra that one or more of these pigments rather than 

 the spirilloxanthin itself are responsible for what activity the carotenoids 

 may have in photosynthesis. 



A particularly interesting situation occurs in Rhodopseudomonas spher- 

 oides, formerly known as Streptococcus varians. This species when 

 grown anaerobically is brown. When grown aerobically, it is bright 

 red. An anaerobic culture may be turned red by shaking with air. The 

 red pigment once formed is not turned back to brown by anaerobic 

 incubation. The nature of this pigment change has been investigated 

 in the live bacteria by French (1940b) and by Van Niel (1947), who 

 isolated the pigments. The absorption spectra of the two pigments 

 obtained from both the brown form and the red form are shown in 



