636 Marine Microbiology 



tained the growth rate through sex^eral liours; the higher concen- 

 trations were inhibitory (Fig. 4). 



Preliminary Results with Other Isolates 



Three other marine isolates, MB 1, MB 21, and MB 29 (10) 

 were tested to determine if the findings with MB 22 were gen- 

 erally applicable. The solutes were tested by comparing the 

 growth rate obtained in 0.3 osmolal NaCl with that obtained in 

 a medium containing the solute, 0.2 osmolal, and NaCl, 0.1 os- 

 molal. Under these conditions KCl was equivalent to NaCl in its 

 effect for each organism. Sucrose and MgCL exerted a sparing 

 effect in only one isolate, MB 21, but inhibitory effects were ob- 

 served using these solutes with the other two isolates. No growth 

 occurred with these organisms in the absence of Na^; Na2S04, 

 0.3 osmolal, replaced and gave a growth response equal to that 

 produced by 0.3 osmolal NaCl for each organism. These results 

 indicated that species variability may have accounted for some 

 of the divergent results reported by previous investigators. 



SUMMARY 



The growth rate of a marine bacterium, Vibrio MB 22 was 

 found to be a function of the concentration of NaCl; the effect of 

 NaCl was on the intact cells and was not the result of preventing 

 cytolysis in the hypotonic solutions. The total growth yield was 

 not regulated by concentration of NaCl; however, in the absence 

 of Na^, no growth occurred. The requii'ement was satisfied by 

 Na2S04, which allowed growth rates equivalent to those obsei"ved 

 in osmotically equivalent concentrations of NaCl. Partial re- 

 placement of the Na^ requirement was accomplished with KCl, 

 MgCL and sucrose; KCl was osmotically equivalent in its effect at 

 all concentrations but MgCL and sucrose were so equivalent only 

 at lower concentrations. At higher concentrations these latter sol- 

 utes were inhibitory and their osmotic effectiveness was masked. 

 The magnitude of the osmotic component of the salt require- 

 ment of Vibrio MB 22 was shown by the occurrence of the max- 

 imal growth rate in 0.1 osmolal NaCl when in the presence of 0.6 

 osmolal KCl; in the absence of the latter salt, 0.4 to 0.6 osmolal 

 NaCl was required. Preliminary experiments with three other iso- 



