Suppression of Bacterial Groivth by Sea Water 575 



g; Tween 80, 8.2 ppm (v/v); and pH 7.0. The sea-water samples 

 were collected from surface, 25, 50, 100, 250, 500, and 535 ( bot- 

 tom) meters. The cultures were grown in 20 x 150 mm tubes, and 

 turbidity recorded at 420 m/- with a Bausch and Lomb "Spec- 

 tronic 20" spectrophotometer. 



( b ) A sea water concentration of 90 per cent ( nine ml added 

 to one ml of stock nutrient Medium II ) was tested with four 

 test bacteria (0.15 ml inocula of 18 hr nutrient broth cultures 

 grown at 30 C). The final concentrations per liter of nutrients 

 were approximately: glucose, 1 g; casein hydrolyzate (NBC), 

 0.02 g; K,HP04, 0.01 g; NH.NO., 0.01 g; pH, 8.0. The sea-water 

 samples were collected from 25, 100, 250, 450, and 980 (bottom) 

 meters. The cultures were grown in tubes and tinbidity recorded 

 at 420 m/t with a Beckman DU spectrophotometer. 



(c) A growth cui^ve was obtained using S. marinoruhra 

 (0.15 ml inoculum of a sixteen hour culture grown at 37 C in nu- 

 trient broth) in 90 per cent sea water supplemented with Medium 

 II. Fifty tubes of each type of sea- water medium were inoculated; 

 three tubes for each treatment were sacrificed at hourly intervals 

 for optical density determinations with the Beckman DU spec- 

 trophotometer. 



RESULTS 



The efi^ect of natural sea water samples, collected ten miles 

 west of San Diego, California (32° 44' N, 117° 25' W) on March 

 1, 1960, compared with artificial sea water using methods (a) 

 and (b) is shown in Figure 1. The values presented are averages 

 of duplicate readings. In Experiment 1, growth of all the fresh- 

 water bacteria was suppressed in natural sea water, except for 

 the case of S. aureus, grown in the surface sample. B. subtilis was 

 the most susceptible to inhibition. Growth of S. miuinoruhra was 

 greatly stimulated by surface sea water, but suppressed by 

 samples from 25, 50, and 250 meters. All of the freshwater species 

 were inhibited most by the bottom sample. 



In Experiment II (Fig. 1), the complex organic additions 

 were reduced and tlie sea-water concentrations increased, in 

 sea-water samples collected 12 miles west of San Diego, California 

 (32° 38' N, 117" 29' W) on May 17, 1960. These sea-water 



