94 Marine Microbiology 



and found able to assimilate organic nitrogen. They are consid- 

 ered important in the degradation of organic matter in contam- 

 inated waters (7). 



Ryther (21) suggested that in an estuary contaminated by 

 wastes from duck farms, the phytoplankton species that became 

 dominant were favored by their ability to use the early products 

 of degradation of organic nitrogenous matter, as well as by their 

 versatility in other respects. It is not easy to assess the influence 

 of soluble organic nitrogenous compounds in other marine en- 

 vironments, however the quantity is not negligible (6, 10). In 

 coastal waters off New England the ratio total nitrogen: total 

 phosphorous is two to twenty times higher than the ratio inorganic 

 nitrogen: inorganic phosphorus (14); inorganic niti"ogen is ex- 

 hausted before phosphate, thus the capacity of an organism to 

 use soluble organic nitrogen might be advantageous at times. 

 The same reasoning holds for the nutrient-poor waters of the 

 Sargasso Sea, where rapid recycling of nutrients takes place ( 18, 

 20). 



The present study compares, in a rough quantitative way, 

 growth rates of a number of species of marine algae when sup- 

 plied either inorganic nitiogen or selected organic compounds. 

 All species were compared on glycine, glutamic acid, glutamine, 

 uric acid and urea, and were tested for their ability to grow on 

 ammonia or nitrite. 



MATERIALS AND METHODS 



The method is outlined as follows. An inoculum of each 

 species was transferred to: 



(1) Sea water enriched with all nutrients except nitrogen 

 (Table 1). 



( 2 ) Sea water enriched as in ( 1 ) but with 100 /<.M nitrate 

 added. 



(3) Sea water enriched as in (1) but with 100 /jM of an 

 organic compoimd added as nitrogen source. 



( 4 ) Enriched sea water as in ( 1 ) with both nitrate and the 

 organic compound (this treatment was omitted in the case of 

 glutamine ) . 



For two organisms, flagellates and 0, 100 rM NHiCl was 

 used instead of NaNOs. 



