582 Marine Microbiology 



Inocula from mesophilic (15-30 C) and "thermophilic" 

 (40-60 C) sites gave rise to typical rhodopseudomonads on incu- 

 bation < 40 C in light. Parallel cultures > 40 C did not grow. It 

 is known that there is a sharp increase in the B12 requirement of 

 Eiiglena gracilis and Ochromonas malhamensis as the environ- 

 mental temperature is raised above optimum (4). Addition of 

 0.1 it(,g% of vitamin B12 to pure cultures of purple bacteria isolated 

 from various sources also permitted some strains to grow at 40- 

 45 C. Studies in procress indicate that most strains of Athiorhoda- 

 ceae produce one or more factors with vitamin B12 activity when 

 cultivated at 25-30 C (5, 7). 



Experiments with R. pahistris indicate that the PABA re- 

 quirement is greater at 40 C than at 35 C. We have also observed 

 that the PABA requirement is not satisfied by folic acid as 

 judged by the excessive concentrations required and the known 

 instability of folic acid. The PABA requirement is spared by 

 products of folic acid and metabolism, e.g., adenine and thymine. 

 The addition of B12 and Ca pantothenate further reduces the 

 PABA requirement (Table 2). These results are reminiscent of 

 sulfanilamide inhibition of growth. But when R. palustris was 

 grown in the presence of low concentrations of sulfanilamide 

 without PABA, growth, surprisingly, was proportional to sulfanil- 

 amide concentration with the range of ca. 1.0 [j^g-lO mg%, sug- 

 gesting that sulfanilamide could replace PABA as a growth fac- 

 tor. No competition was observed between PABA and sulfanila- 

 mide when the latter was supplied in growth-promoting con- 

 centrations. At higher concentrations of sulfanilamide (ca 0.1- 

 0.4%) growth was inhibited; under these conditions, supra-optimal 

 concentrations of PABA were required to restore growth. The 

 requirement for vitamin Bvz which emerges in R. palustris at 

 elevated temperatures may be related to its PABA requirement, 

 since less PABA was required when vitamin B12 was supplied. 



Aromatic Compounds as Substrates for Purple Bacteria 



Growth of anaerobic R. palustris cultures containing benzoic 

 acid as sole substrate was strictly light-dependent. At limiting 

 substrate concentrations of benzoate, growth was proportional to 

 concentration. Growth experiments with strains of the five species 



