Stimulation of Growth of Desulfovibrio dcsulfuricans 449 



tically suppressed as compared with tliose in the remaining media. 

 These facts suggest that the pattern of the amino acid require- 

 ment in these four strains differed to a certain extent from that in 

 strain Maizuru 1. 



TABLE 6 



Growth of Various Strains of D. Desulfuricans in the Defined Medium 

 Based on Minerals, Lactate, Ascorbic Acid and ATP, and Supplemented 

 WITH Amino Acids or Casamino Acids or Peptone, as Nitrogen Sources 



Growth (O.D. at 610 m/x) in the Medium Supplemented With: 



Casamino 18 Amino 13 Amino 



Peptone 



Strain 



A cids 



Acids 



A cids 



*Fresh-water strain. 

 **Salt-water strain. 



The population densities obtained with the cultures of the 

 salt-water strains ( El Agheila Z and Maizuru 1 ) at the maximum 

 growth phase were generally higher than those of the fresh- 

 water strains (Wandle, Hildenborough and Miyazaki), especially 

 in the cases that chemically defined media were employed. The 

 times required for attaining the maximum growth of the salt- 

 water strains were also more or less shorter than those of the 

 fresh-water strains. These may be due to the lower concentra- 

 tion of NaCl in the fresh-water medium as compared with that in 

 the salt-water medium; certain heavy metals which probably 

 contaminated to reagent NaCl might be responsible for tlie 

 stimulation of growth of these microorganisms to some extent. 



CONCLUSION 



The general conclusion wliich can be drawn from all these 

 experiments is that most of sulfate-reducing bacteria belonging 

 to genus Desulfovibrio, irrespective of their response to the NaCl 



