Studies on the Ecology of a Marine Spirillum 565 



The present study was confined to the growth of a heterotrophic 

 marine Spirillum in a chemostat at low concentrations of the 

 growth-hmiting nitrogen source. Complete wash-out of the pop- 

 ulation, believed to indicate the lower limit of quantitative re- 

 quirements, occurred in concentrations of 0.14 mg asparagine- 

 N/L or less. This value depends on tlie arbitraiy choice of the 

 dilution rate (D = i /u,. = 0.185 hr~^). The experimental value 

 was found to be considerably higher than the theoretical value. 

 This suggests the existence of an absolute threshold concentra- 

 tion of the growth-limiting nutrient at the lowest possible dilution 

 rate. 



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