STUDIES OF COLIFORM BACTERIA IN THE SEA 



65 



When natural, unpolluted sea water is brought into the laboratory and 

 stored in the dark a tremendous growth of the bacterial population takes 

 place. This growth and the effect of adding E. coli to the water are shown 

 in Figure 1.* The total population of the raw sea water increases to a 

 maximum in three days, then decreases to a more or less uniform popula- 

 tion of about a million cells per ml. A slight initial increase in bacterial 

 numbers is also detected in the water to which the coliforms were added. 

 This period of growth of the mixed population is followed by a decrease 

 in numbers so that the final populations are approximately the same 

 whether E. coli were added or not. 



O-Tolot Bocl*rlo la Ro« S*a WaUr 



Tola) Baettria in Ra« Sao Water 

 Inacvlalad aiiK 10* f.^// /cc 



J L 



Time in Days 



Fig. 1. Growth of marine bacteria 

 and the viabihty of Escherichia coli in 

 untreated sea water. 



The concentrations of E. coli were estimated independently in this 

 experiment by inoculating lactose broth fermentation tubes. The indicated 

 numbers of E. coli thus obtained are also shown in Figure 1. They decrease 

 regularly from the initial inoculum of 10^ cells/ml and after approxi- 

 mately seven days only a millionth of this population persists. Clearly, 

 the conditions which are suitable for the growth of marine bacteria are 

 inimical to the growth or persistence of the coliforms. It appears that the 

 final populations in both the raw sea water and in the water inoculated 

 with E. coli consist of the normal sea water organisms. 



If, instead of using untreated sea water, Escherichia coli are intro- 



* The numbers were determined by plate counts after 7 days' growth on a medium 

 containing 1 gm glucose, 1 gm peptone, 0.05 gm NaH2P04, 15 gm agar in 1 liter of 

 aged sea water. 



