STUDIES OF COLIFORM BACTERIA IN THE SEA 67 



TABLE I 



Average Coefficients of Death Rate of Escherichia coli 

 IN Sea Water Treated in Various Ways 



value. Thus, a coefficient of 1.0 means that a tenth of the population dies 

 daily; the coefficient 0.04 indicates that 20 days are required for an 

 equivalent mortality. These experiments show that sea water has a potent 

 bactericidal action. The activity is decreased greatly by autoclaving, but 

 not by boiling the sea water. It is increased by previous "pollution" of 

 the water with E. coli. 



Further investigations are necessary to determine how the bactericidal 

 activity of sea water varies with natural conditions. Is there a seasonal 

 variation which might be correlated with variations of the normal popula- 

 tion of the sea? Is the bactericidal activity greater in polluted harbors 

 than in the open sea, and what are the effects of dissolved organic matter, 

 oxygen supply and other variables associated with pollution? What is the 

 identity or nature of the bactericidal activity? 



Some of our experiments suggest that antibiotic substances produced 

 by marine organisms may be responsible for the death of the pollution 

 bacteria. They do not exclude, however, the possibilities that bacteri- 

 ophage or autolytic or degenerative products of the coliforms themselves 

 may also be involved. It is possible that all three contribute to the final 

 action. It is significant, however, that Rosenfeld and ZoBell (1947) have 

 recently described the production of antibiotic substances by several species 

 of marine bacteria. None of these antibiotics was inimical to gram nega- 

 tive species and E. coli was not included among their test organisms. In 

 our experiments pour plates of the normal sea water bacteria were made 

 and the population allowed to develop for 48 hours. The surface of one 

 of each pair of plates was then flooded by a suspension of E. coli, the excess 

 being poured off. After a total time of four days the plates were inspected 

 and clear areas were found surrounding some of the sea water bacteria. 

 These results suggest that some of the sea water forms produce substances 

 inimical to E. coli. 



It is pertinent to inquire whether the results of these laboratory experi- 

 ments bear any relation to the phenomena which occur in nature. In the 

 sea the mortality of the bacteria may be completely obscured by the cir- 

 culation and mixing of water masses. The dilution of the polluted water 



