146 



Marine Microbiology 



inoculated into these media and allowed to grow at 30 C on a 

 shaker for twenty-four hours. The calculated optical density of 

 bacterial growth was detemiined. Typical results obtained for 

 several bacteria are presented in Figure 5. Excellent growth of 

 isolate M4, obtained from the water where the bloom was 

 collected, is shown by the steadily rising growth in proportion 

 to the concentration of diatomaceous extract supplied in the 

 medium. Other bacteria, obtained from remote geographic loca- 

 tions, were unable to take advantage of the organic substrate 

 beyond the lowest concentrations, presumably because of the 

 inimical effects of the antibacterial substance present in the 

 diatoms. 



TABLE 5 



Growth Promotion and Inhibition of Bacteria by Phytoplankton (Chief- 

 ly Skeletonema costatum) from Long Island Sound and by Gonyaulax tam- 

 arensis from La Parguera, Puerto Rico. Radial Zones of Inhibition (Inside) 

 and Larger Radii of Promotion are Recorded in mm. — =No. Record. 



* YBA signifiics Difco yeast beef agar. 

 ** Formula for Medium A is given in Table 1. 

 *** Formula for Medium B is given in Table 1. 



It has been found, also, that many bacteria isolated from 

 the marine environment produce antibiotic substances that are 

 very active against marine bacteria and algae, as well as against 



