Suppression of Bacterial Growth by Sea Water 577 



natural sea water from 100 meters (32° 41' N, 117° 25' W) col- 

 lected on May 17, 1960. Although the lag phase was slightly shor- 

 ter, the final turbidity in the natural sea-water medium was less 

 than in artificial sea water. This result has been confirmed many 

 times in similar experiments. 



Other data indicated that samples of natural sea water stored 

 at 4 C gradually lost their inhibitory effect, presumably due to ad- 

 sorption of toxic substances on the walls of the glass containers. 

 The observations of ZoBell and Anderson (23), which indicated 

 an increase of marine bacteria stored in containers, may have in- 

 volved not only the concentration of naturally occurring organic 

 matter, but also the removal of inliibitory sul:)stances by the addi- 

 tion of a glass-water surface. 



DISCUSSION 



The results indicate that sea water varies in its ability to 

 support the growth of bacteria, depending upon where and when 

 it is collected, and on the species concerned. Natural sea water, 

 in comparison to artificial sea water, usually suppressed the 

 growth of freshwater bacteria, and sometimes even that of the 

 marine bacterium S. marinoruhra. These growth studies confirm 

 previous observations on the generally adverse effect of natural 

 sea water on the survival of pollution and other freshwater bac- 

 teria, e.g., see Scarpino, Carlucci, and Pramer (16). 



Artificial sea water may not be a suitable standard for com- 

 parison of growth with natural sea water. Although not stressed 

 by the autliors, it was shown by MacLeod and Onofrey (10) 

 that in most cases marine bacteria developed better in artificial 

 sea water than in natural sea water under similar experimental 

 conditions. The major constituents of artificial sea water are 

 similar to natural sea water, but the trace elements and growth 

 factors are not identical. Growth suppression by natural sea 

 water may be caused by traces of toxic ions, or slight shifts in 

 redox potential. 



SUMMARY 



Terminal growth of various freshwater and marine bacteria 

 (Bacillus subtilis, Escherichia coli, Micrococcus hjsodeikticus, 



