Some Nutritional Relationships Among Microbes 145 



It is of considerable interest to know what use can be made 

 of this vast amount of organic matter assembled in the cells 

 of diatoms possessing antibacterial activity. Accordingly, hot 

 aqueous extracts of the diatoms were prepared in sea water and 

 a series of media were made so as to contain different amounts 

 of extract in the range from 1.4 to 22.0 grams per liter. Bacteria 

 obtained from Long Island Sound and from Puerto Rico were 



^ 5 10 15 20 25 



DIATOM EXTRACT- MG PER ML 



Fig. 5. Growth responses (after 24 hr.) of marine bacteria cultivated in 

 sea water containing different concentrations of an aqueous extract pre- 

 pared from a bloom of tlie diatom, Skeletonema costatum, taken from 

 Long Island Sound, February, 1961. Note that bacterium M4, isolated 

 from the plankton bloom, grows very well, whereas other isolates appear 

 to be inhibited by antibiotic acti\'ity of the diatoms (compare Table 4). 



