Some Nutritional Relationships Among Microbes 143 



of test plates of vitamin-requiring bacteria. Zones of growtli pro- 

 motion indicate that a supply of required \ itaniin produced by 

 the algae has diffused into the seeded agar plate, where stimula- 

 tion of the vitamin-deficient bacteria occurs. 



Although it is beyond the scope of this discussion to present 

 all of our observations concerning various effects of marine algae 

 upon growth of bacteria, it can be stated tliat macro-algae, as 

 well as planktonic dinoflagellates and diatoms, produce special 

 substances with both inhibiting and promoting properties for bac- 

 teria. The antibacterial action of red algae and certain dinoflagel- 

 lates has already been emphasized ( 3 ) . Some typical results that 

 have been obtained in recent tests of the effects of extracts from 

 tropical and temperate blooms of phytoplankton on seeded plates 

 of four laboratory strains and ten isolates of marine bacteria are 

 presented in Table 5. The Gomjaulax (identity not certain) "red 

 tide" was collected in Puerto Rico during January, 1961 and the 

 plankton bloom of Skeletoiiema was obtained from Long Island 

 Sound in February, 1961. When these crude plankton materials, 

 and other marine algae, were placed upon seeded Difco yeast 

 beef agar plates, inhibition zones occurred around the algal 

 material and striking circular zones of heavier growth were 

 formed beyond. In specially prepared agar plates lacking single 

 vitamins and seeded with marine bacteria that require these 

 vitamins, pronounced zones of inhibition frequently occurred, 

 and usually marked stimulation of growth was observed in the 

 form of halos around the points where the algae were applied 

 ( Fig. 4 ) . Such results may be explained by the diffusion of anti- 

 bacterial substances outward to cause zones of inhibition, and 

 further diffusion of B vitamins beyond these zones of inhibition 

 to produce halos of growth in \ itamin-deficient agar. It can also 

 be demonstrated that algae supply complete sources of carbon 

 and nitrogenous materials for growth of marine bacteria. 



The production of a diatom bloom in Long Island Sound 

 occurs regularly ever\^ February, as a result of the increased 

 phosphate, nitrate, vitamin Bil, and sunlight at this time of the 

 year (13). So pronounced is the bloom that the above listed 

 factors which contributed to it, except sunlight, are removed from 

 the water by the first of March. Since vitamins of the Bn- group 



