486 Marine Microbiology 



did not require Na^ from organisms which did and since non- 

 sodium requiring organisms are prevalent in the laboratory en- 

 vironment, special precautions had to be taken to avoid contam- 

 ination. Cell suspensions v^^ere irradiated in a sterile quartz flask - 

 which accounts for the length of the irradiation time required 

 to achieve an appreciable kill. I may also say that many attempts 

 were made to increase the yield of mutants by increasing the ir- 

 radiation dosage, but none of these attempts succeeded. We 

 either got no mutants or a few which failed to survive on sub- 

 sequent transfer. 



The response of three of these mutants to Na^ in a chemically 

 defined medium prepared with purified components is compared 

 with that of the parent culture. Table 4. It is evident that whereas 

 the original culture failed to grow in the absence of Na^, the 

 three isolates grew appreciably under these circumstances. All 

 three however, grew more extensively when Na^ was added to 

 the medium. 



TABLE 4 



Comparison of the Na+ Response of Organism B-16 and Three Mutants 

 Derived From it by Ultra-violet Irradiation 



M B-16 Mutant A: Mutant Bs Mutant C, 



Incubation Time (Hrs.) 

 22 72 192 22 72 192 22 72 192 22 72 192 

 Per Cent Transmission* 



* Evelyn colorimeter readings, 660 m/i filter. 



A total of 14 isolates have been obtained by ultraviolet 

 irradiation (capable of growing) in tlie chemically defined me- 

 dium without Na^ added. These were compared morphologically 

 and in biochemical tests employing standard methods with the 

 original culture of organism B-16 and with B-16 adapted to grow 



