Organic Sources of Nitrogen for Marine Centric Diatoms 101 



Toxicity and Other EflFects 



The following were somewhat inhibitory in the presence of 

 nitrate: glycine to Coccolithus huxleyi, uric acid to Cyclotella 

 caspia and clone BT-6 of C. Huxleyi; urea to Chaetocews peJagi- 

 ciis and Skeletonema costatum. Growth of clone BT-5 of C. 

 huxleyi was delayed (again in the presence of nitrate) by all 

 organic sources for about two days, but final yields were about 

 the same as in nitrate alone. The green alga BT-2 (Carteria?) 

 also showed a delay but finally grew excellently on uric acid. 



In a few experiments the inoculum died on transfer to an 

 organic N source alone (i.e., without nitrate); in some cases when 

 the source was known from other experiments to be utilizable. 

 This occurred more frequently when the inoculum was small, 

 severely depleted, or put into strong light. Some species may 

 only survive and grow at low light intensity if given a N-source 

 that is assimilated slowly. This would be significant ecologically, 

 but has not been investigated. 



Urea and uric acid brought about morphological changes in 

 a few species. Cyclotella caspia cultures grown on uric acid were 

 much darker in color than those supplied nitrate. The amount of 

 chlorophyll a per cell was much larger in the uric acid grown 

 cells than in nitrate grown cells, though the cell volumes were 

 only slightly larger. In one experiment the values were 71 X 1(H 

 /ig/cell in uric acid and only 3.6 X IQ-s /xg/cell in nitrate. This 

 effect on chlorophyll a content was not noticeable with other 

 species, but no measurements were made. McLachlan and Yentsch 

 (16) noted that peptones increased chlorophyll production by 

 Dunaliella teriiolecta (see this reference for methods). 



DISCUSSION 



Harvey's conclusion (11) that the simple amino acids do 

 not serve directly as a source of nitrogen for marine algae is 

 confirmed, with the notable exception that the bottom-dwelling 

 diatoms Coscinodiscus asteromphalus and Melosira (0-8) used 

 glutamate and glutamine as readily as inorganic nitrogen in these 

 experiments. Possibly these species have heterotrophic leanings. 

 Bruchmayer-Berkenbusch (3) reported that amino acids influ- 

 enced auxospore formation in Melosira nummuloides. 



