TETRAPYRROLES 37 



The amount of bacteriochlorophyll in the Athio- and Thiorhodaceae 

 is of a similar order to that found in algae (Table 1), In the Athiorho- 

 daceae, the conditions under which the organisms are grown can cause 

 quite marked changes in the concentration of bacteriochlorophyll. 

 Apart from factors such as light intensity and oxygen tension (to be 

 discussed later) the carbon source also influences bacteriochlorophyll 

 synthesis (7,8), Iron deficiency causes a marked decrease in bacterio- 

 chlorophyll content and this metal seems to be involved in the bio- 

 synthesis of all forms of chlorophyll. Formation of Chlorobmm chloro- 

 phyll is diminished by lack of iron (9) and there are numerous ex- 

 amples of iron-deficiency chlorosis in higher plants (10). 



TABLE 1 

 Bacteriochlorophyll content of some photos ynthetic bacteria 



Organism Carbon source 



Bacteriochlorophyll 

 (m/imoles/mg dry wt) 



Athiorhodaceae 



R. rubnim Malate 13 



NCIB no. 8255 



Rps. spheroides Malate 12 



NCIB no. 8253 



Rps . palustris Malate 11 



2.1.7 



Rps. capsidata Succinate 22 



2.3.11 



Thiorhodaceae 



Thiopedia sp. CO2 16 



Chromatium D CO2 24 



Succinate 33 



Data from Kornberg & Lascelles (8) and from unpublished personal observa- 

 tions. All cultures were grown anaerobically under a light intensity of about 

 250 ft-c and estimations were made when the culture density had attained a 

 density of 0.6-1.0 mg dry wt/ml. 



Cytochromes and catalase. 



The contribution to the total tetrapyrroles made by the prosthetic 

 groups of cytochromes and catalase is slight (about 1%) compared 

 with that made by the chlorophylls (Table 2), Even the high catalase 

 mutant of Rps. spheroides (11), of which catalase comprises 5-25% of 

 the dry weight, contains only about 0,5-2,4 m^mole/mg dry weight of 

 tetrapyrrole (calculated as catalase heme), Athiorhodaceae grown in 



