632 



Marine Microbiology 



was concluded that the effect of NaCl was to control the growth 

 rate of the intact cells of MB 22. 



Q. 



o 



24 HR 



7 HR 



4 HR 



02 0.4 0.6 0.2 0.4 06 



NaCi ( MOLES PER LITER ) 



Fig. 1. la EflFect of the concentration of NaCl on the growth rate and 

 growth yield of Vibrio MB 22. lb. Effect of the concentration of NaCl. in the 

 inoculum culture on the subsequent response of the cells to NaCl. Inoculum 

 was grown in 0.4 M NaCl (open circles). Inoculum was grown in 0.05 M 

 NaCl (closed circles). Incubation seven hours. 



Replacement of NaCI with NasSOi 



Although NaoSOi was not a suitable salt to test the specificity 

 of the Na"^ requirement, it was useful in determining the character 

 of the response since it differs from NaCl in both its colligative 

 activities and ionic strength, allowing comparisons to be made 

 on both bases. MacLeod and Hori (5) have reported media of 

 suitable ionic strength to be essential to the activity of cell-free 

 preparations of isocitric dehydrogenase and aconitase isolated 

 from a marine bacterium. The Na^ requirement for MB 22 was 

 satisfied by Na2SOi; equivalence with NaCl was found when the 

 results were compared on an osmolal basis (Fig. 2). Thus, 0.16 

 molal NaCl and 0.13 molal Na.SOi produced an equivalent os- 

 molality of 0.3. This equivalence suggested that at these concen- 

 trations the principal factor controlling the growth rate was tlie 

 tonicity of the medium. 



