484 Marine Microbiology 



gressively more feeble on being successively transferred into 

 media containing the same low Na* concentration. On the fourth 

 or fifth transfer at the 0.02M Na* level growth failed to occur. 

 The other organisms behaved similarly. This obsen^ation is in 

 agreement with that of other investigators who have also failed to 

 train marine bacteria to grow at appreciably lowered sea water 

 or Na"^ concentrations. 



By plating heavy suspensions of marine bacteria on trypti- 

 case medium prepared without added Na"^, Pratt and Waddell 

 ( 5 ) obtained a few colonies which they assumed were mutants of 

 marine bacteria which no longer required Na* for growth. 



We were unable to obtain colonies of our organisms under 

 similar conditions but found that one of the organisms, B-16, 

 could be trained to grow well on the trypticase agar medium 

 containing no added NaCl if it was streaked serially onto the 

 surface of plates of the medium containing progressively lower 

 concentrations of Na"^. 



A flame photometric analysis of the trypticase medium pre- 

 pared without added NaCl revealed a concentration of 0.028M 

 Na"^ present as a contaminant. By comparison, the chemically de- 

 fined medium used in these studies contained only 6.5 x 10"^M 

 Na\ 



Since the culture of organism B-16 adapted to grow in the 

 trypticase medium without added NaCl was actually growing at 



TABLE 2 



Comparison of Na+ Response of B-16 and of B-16 Adapted to Growth on 

 Trypticase Agar Without Added Na*- 



* Evelyn colorimeter readings, 660m/x filter. 



