Organic Sources of Nitrogen for Marine Centric Diatoms 103 



diatoms, one pennate diatom, two estuarine flagellates, an oceanic 

 green flagellate, and tln^ee coccolithopliorides. 



The two estuarine flagellates used only ammonia among the 

 inorganic N-sourccs; the other algae used nitrate and nitrite as 

 well. While most organic sources allowed some growth above 

 that in the N-free medium, the alpha amino acids were generally 

 poor, except that the bottom-dwelling diatoms Melosira and 

 Coscinodiscus grew as well on glutamate as on nitrate. Glutamine 

 was a somewhat better source in general. Urea and luic acid 

 were consistently better for most estuarine and neritic clones, 

 but not for the oceanic ones. 



There was no evidence that naturally occurring organic ni- 

 trogen in the sea water employed was used bv any algae. 



Evidence suggests that direct utilization of uric acid may be 

 significant in some environments. 



ACKNOWLEDGMENTS 



I am grateful to Miss Elizabeth Alt and Mrs. Yolande Kahler 

 for assistance with many of the experiments. Some of the organ- 

 isms were isolated through the use of facilities of the Bermuda 

 Biological Station. I thank Mr. Ralph Vaccaro and Mr. Jon Thun- 

 berg for measuring the inorganic nitrogen content of the sea 

 water used. 



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