Osmotic Regulation of the Growth Rate 



633 



09 



_ 0.6 



CO 



z 



UJ 



o 



0.3. 



2a 



2b 



02 0.4 0.6 



OSM OLAL CONC 



02 04 0.6 



IONIC STRENGTH 



Fig. 2. 2a. Comparison on an osmolal basis of the effect of NasSOj and 

 NaCl on the growth of Vibrio MB 22 after five hours incubation. Na2S04 

 (open circles). NaCl (closed circles). 2b. Comparison of the same data 

 but with ionic strength plotted on the abcissa. Na^SOi (open circles). NaCl 



(closed circles). 



Partial Replacement of NaCl by KCl or MgCL 



Neither KCl nor MgCL wholly replaced the Na"^ require- 

 ment; however, in the presence of suboptimal concentrations of 

 NaCl the growth rate of MB 22 was enhanced by either of these 

 salts. Approximately 0.1 osmolal NaCl was required to produce 

 the maximal growth rate in the basal medium containing 0.6 os- 

 molal KCl. In the absence of the latter salt four or five times 

 as much NaCl was required. The effectiveness of KCl was tested 

 in the presence of 0.125 osmolal NaCl and was found to give 

 growth responses equivalent to NaCl at all concenti^ations tested 

 (Fig. 3a). The lower concentrations of MgCL were as efiFective 

 as NaCl when their activities were compared on an osmolal basis; 

 however, higher concentrations depressed the growth rate (Fig. 

 3b). The effectiveness of MgCL was of significance since it is a 

 three ion salt whose colligative properties do not depart greatly 

 from the ideal at the concentrations used; hence, the function of 

 Na"^ was in part replaced by Cl~ when MgCL was employed. The 



