586 Marine Microbiology 



bacteria under anaerobic conditions provides evidence that a 

 hydrogen acceptor— in this instance, a photochemical oxidant— 

 can substitute for molecular oxygen. 



The present enrichment-isolation procedure for R. palustris 

 combines selective illumination, selective substrate, and a selec- 

 tive growth factor, with superposition of vitamin Bn. and temper- 

 ature representing a fourth selective factor of sorts. Quite likely 

 this procedure selects for only one set of strains of R. palustris— 

 those utilizing benzoate; the species-specific substrate, if existing, 

 remains unknown. 



SUMMARY 



An anaerobic enrichment procedure for isolating Rhodo- 

 pseudomonas palustris is described in which the specific require- 

 ment for p-aminobenzoic acid and the photosynthetic utilization 

 of benzoic acid exclude other members of the Athiorhodaceae. 

 Nutritional experiments with elective cultures and pure cultures 

 of R. palustris indicate an increased requirement for p-amino- 

 benzoic acid when incubated > 40 C. In addition, a requirement 

 for vitamin B12 is superimposed at elevated temperatures. The re- 

 quirement for PABA was not satisfied by folic acid and was 

 spared by certain products of folic-catalyzed reactions. Low con- 

 centrations of sulfanilamide also satisfy the PABA requirement. 

 Aromatic substrates such as benzoic acid can be utilized by 

 representative species of rhodopseudomonads and at least one 

 rhodospirillum. 



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