584 



Marine Microbiology 



400 r 



300 



Q. 



13 



;$! 200 - 



100 - 



2JJ.IVI BENZOATE 



IjiM BENZOATE 



ENDOGENOUS 



100 



200 



MINUTES 



300 



Fig. 1 Oxygen consumption by cells of Rhodopseudomonas palustris or 



RhodospiriUum ruhrum grown on Na benzoate as sole substrate under 



anaerobic conditions in the light. 



PABA, seemed highly selective in excluding purple bacteria 

 other than R. palustris. By analogy, a specific enrichment for 

 R. ruhrum might be devised by taking advantage of its require- 

 ment for biotin. Similarly, the requirement for vitamin B12 which 

 emerges at elevated temperatures may represent an additional 

 selective factor to be exploited in searching for thermal auxo- 

 trophs among the purple bacteria. 



Preliminary studies with single strains of the obligate anaer- 

 obes RhodospiriUum photometricum and RhodospiriUum molis- 

 chianum indicate that these purple bacteria can be cultivated in 

 synthetic media when given B vitamins such as biotin or nico- 

 tinic acid along with PABA. The frequent requirement for vita- 

 min B12 in other photosynthetic microorganisms and the absence 

 of B12 requirements in photosynthetic bacteria had appeared to set 



