Osmotic Regulation of the Growth Rate 635 



addition of 0.2 per cent succinic acid resulted in growtli and the 

 maintenance of a neutral pH in the presence of sucrose; tliis 

 concentration (0.017 M) did not contribute significantlx' to tlie 

 osmolality of the medium. The growth rate of isolate MB 22 was 

 enhanced by the addition of sucrose to a medium containing suc- 

 cinate and optimal amounts of NaCl. The concentration of su- 

 crose required for maximal stimulation was 0.1 per cent, again 

 an amount not contributing significantly to the osmotic activity 

 of the medium. In view of these results 0.1 per cent sucrose and 

 0.2 per cent succinic acid were added to the basal medium; the 

 addition of optimal amounts of NaCl to this medium resulted in 

 a rate of growth which was not increased by the further addition 

 of sucrose. Growth did not occur in this new basal medium with- 

 out the addition of Na"; however, sucrose caused an appreciable 

 stimulating effect in the presence of 0.1 osmolal NaCl. The lower 

 concentrations of sucrose were equivalent to NaCl and main- 



OSMOLAL CONC 



TIME ( HOURS ) 



Fig. 4. Partial replacement of tlie growth requirement for NaCi by sucrose 

 using Vibrio MB 22. NaCl, 0.1 osmolal; succinic acid, 0.2 per cent; and 

 sucrose, 0.1 per cent were added to the basal medium. 4a. Comparison of 

 growth in sucrose and NaCl after five hours. Sucrose (open circles). NaCl 

 (closed circles). 4b. Comparison of growth rates in 0.2 osmolal sucrose 

 and 0.2 osmolal NaCl (total osmolality, 0.3). A. 0.3 osmolal xNaCl; B. 0.2 

 osmolal sucrose, 0.1 osmolal NaCl; C. 0.1 osmolal NaCl. 



