Chapter 59 



Osmotic Regulation of the Growth Rate 

 of Four Species of Marine Bacteria* 



Darrell Pratt and Mary Austin 



xX number of marine bacteria have been reported to require 

 relatively high concentrations of Na"^ for their optimal growth 

 and metabolic activity; this requirement has been considered to 

 be more than a simple expression of osmotic activity since the 

 total replacement of Na^ with nonspecific solutes has not been 

 successful (4, 6, 8, 9, 10). The possibility that Na"^ plays some 

 osmotic role has been demonstrated by the partial substitution 

 of sucrose for NaCl in metabolic and growth experiments. The 

 results of these latter experiments have been variable and the 

 degree of replacement has been low; consequently, the osmotic 

 function of Na^ has been considered a minor one by some workers. 

 However, failure to replace an effective solute by a nonspecific 

 solute must be interpreted with caution since the technic has 

 several hazards. The solutes selected, in addition to being os- 

 motically effective, must also not have stimulatorv or inhibitory 

 effects on the test organism in the experimental circumstance. 

 The stringent nature of these demands is evident since they re- 

 quire the substance to have little or no secondaiy biological ac- 

 tivity at relatively high concentrations. Thus, the Na"^ require- 

 ment of a marine bacterium could be largely osmotic in character 

 and still be relatively specific because of the cell's intolerance 

 for other solutes at osmotically equivalent concentrations. This 

 report deals with the results of a study of the osmotic function of 

 Na* in the growth medium for a Ijacterial isolate of marine origin. 

 One objective was to determine if osmotic equivalence of solutes 

 could be observed with suboptimal concentrations, an equi\'alcnce 



* This work was supported in part by Grant 0-7075 from the National Science 

 Foundation. 



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