Belser, 1957) • The significance Of these com- 

 pounds in the ecology of the sea is strongly 

 implied by the experiments presented in this 

 paper . 



Amino-acid pools stimulated "both C^Og 

 uptake by the phytoplankton and bacterial 

 development (Table 17) • Some marine bacteria 

 have been shown to require certain amino acids 

 (Ostroff and Henry, 1939; MacLeod et al., 195^; 

 Jones, 1957). In addition, Fogg (1952J 

 reported that the blue-green alga, Anabaena 

 cylindrica , produced equal amounts of 

 extracellular and intracellular polypeptide 

 nitrogen. It is highly probable that 

 proteinaceous compounds in the sea exert 

 considerable influence on the mutual 

 interrelationships between marine phyto- 

 plankton and bacteria. 



The great increase in C^-^t^ assimilation by 

 the phytoplankton in the presence of 0.001°/ o 

 of the surface active agent, Tween 80, 

 (Table 17) which was not confirmed by a later 

 experiment (Table l8) will require further 

 consideration. It is of interest to note 

 that the bacterial numbers were increased 

 markedly in both experiments in the presence 

 of the Tween 80. Inorganic additions did 

 not appear to enhance C^02 fixation or 

 bacterial development appreciably. This may 

 be due to a lack of organic growth factors in 

 tropical Pacific sea water rather than to a 

 limitation of inorganic nutrients. 



The exposure of the phytoplankton in the sea- 

 water samples to the NaHCl^K^ for short 

 periods of time (2 to h hours) may not have 

 been sufficient to allow appreciable 

 differences in Cl^C>2 assimilation to take 

 place in all cases. If the cells were 

 deficient in one or more of these nutrients, 

 it might take some time for uptake to be 

 reflected by the photosynthetic mechanism. 

 For example, it takes about 2h hours for 

 Scenedesmus cells to recover from nitrogen 

 deficiency to the extent of containing the 

 amount of protein found in normal cells 

 (Thomas and Krauss, 195*0 • However, in the 

 present work short experimental periods were 

 chosen so that photosynthesis could be 

 measured without measuring phytoplankton 

 growth. In subsequent experiments of this 



type the times could be varied. 



The importance of dark-bottle controls for all 

 treatments in experiments of this type is 

 evident from an examination of any of the values 

 obtained for dark fixation compared with light 

 fixation. This conclusion is supported by that 

 of Jones et al. (this volume). 



These experiments provide preliminary informa- 

 tion from the natural environment which can be 

 used for future detailed culture and 

 photosynthetic experiments in the laboratory. 

 For instance, the development of culture media 

 for pelagic phytoplankton and marine bacteria 

 might be facilitated by the inclusion of some 

 of these substances, especially purines, 

 pyrimidines and amino acids, in the media. 

 Specific effects of these substances on the 

 photosynthetic mechanisms of the phytoplankton 

 and requirements by the bacteria may be 

 determined in pure culture . 



ACKNOWLEDGEMENTS 



The authors would like to express their sincere 

 appreciation to Dr. William L. Belser, Scripps 

 Institution of Oceanography, for his help in 

 formulating the organic constituents tested and 

 for critically reviewing the manuscript. In 

 addition, the authors would like to thank 

 Mr. Donald W. Lear and Mr. Harold L. Scotten, 

 Scripps Institution of Oceanography, for their 

 help in preparing for the cruise. 



BIBLIOGRAPHY 



Belser, W. L. 1957. 



The use of auxotrophic mutants of a marine 

 bacterium for the bioassay of organic 

 micronutrients in the sea. Bacteriol. 

 Proc, pp. 30. 



Dam, H. I9M4. 



Vitamin K in unicellular photosynthesizing 

 organisms. Amer. Jour. Bot., Vol. 31, 

 PP. l4-92-i4-93- 



Droop, M. R. 1957. 



Auxotrophy and organic compounds in the 

 nutrition of marine phytoplankton. Jour. 

 Gen. Microbiol., Vol. 16, pp. 286-293. 



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