1188 THE LIGHT FACTOR. III. COLOR CHAP. 30 



bacteria are particularly favorable for an investigation of the part played 

 by the carotenoids in photosynthesis, since the absorption peaks of the 

 bacterial carotenoids are not concealed behind the absorption bands of 

 chlorophyll, as is the case not only in green plants, but also in "fucoxanthol 

 algae." 



Table 30.VIII 



Position of Wave Length Maxima (m/x) in Spectrum of Streptococcus varians 



(after French 1937) 



Methanol solution Cells Action spectrum 



410 420 — ~~ 



— 490" — 



— 510" — 



— 550" — 

 605 590 590 ' 

 770 880 900 



° Carotcnoid bauds. 



Vermeulen, Wassink and Reman (1937), too, found that the develop- 

 ment of Chromatiuni takes place mainly in light belonging to the absorp- 

 tion bands of bacteriochlorophyll (infrared, red and a narrow band at 590 

 mju; cf. figs. 22.19 and 22.21), but not in those of the red carotenoid pig- 

 ments. 



More recently, however, Manten and Thomas found the situation to be 

 more complex. First, Manten (1946), in studying the action spectrum of 

 phototaxis of Rhodospirillum ruhrum, found peaks corresponding to the 

 absorption peaks of bacteriochlorophyll (590 m/x) as well as to those of some 

 of the carotenoids (but not the main carotenoid of these cells, spirilloxan- 

 thol). He suggested that the mechanism of phototaxis involves in Rhodo- 

 spirillutN, primarily, a stimulation of photosynthesis, and that the action 

 spectrum of phototaxis therefore indicates that some (but not all) caro- 

 tenoids are photosynthetically active also in purple bacteria. Thomas 

 (1950) investigated the action spectrum of photosynthesis of the same cells 

 manometrically by measuring carbon dioxide consumption in the presence 

 of 0.015 M sodium butyrate as hydrogen donor, (cf. chapter 5, p. 106). Be- 

 cause of the sigmoid shape of the light curve, the action spectrum was 

 determined by measuring the ratio of ACO2 in light of a given wave length 

 (bands isolated by Christiansen filters) to ACU-j in light of a standard wave 

 length (yellow sodium line) . Between 460 and 650 mii the action spectrum 

 had a peak at 590 m^ belonging to bacteriochlorophyll (see fig. 22.27) 

 and three peaks attributable to carotenoids. However, no maximum of 

 photosynthesis is noticeable at 550 m^u, whore a peak is present in the 

 absorption curve of the cells (compare fig. 22.27 and table SO.VHI above) ; 

 this peak has been attributed to the most abundant bacterial carotenoid, 



