Nutritional Patterns in Marine Bacterial Populatio?is 693 



this group to tlie sources of free amino acids in surface waters. 

 Decomposing organisms and residues, dissolved organic matter 

 and the excretions of other organisms all contribute to meeting 

 the organic nitrogen needs of planktonic bacteria. However, 

 Waksman et ah (23) noted tliat much of the nitrogenous material 

 of phytoplankton origin undergoes rapid decomposition in the 

 sea and it is likely that compounds such as amino acids will be 

 more readily available in upper levels of the ocean where there 

 may be a continuing supply of tliem. In view of the fact that tlie 

 majority of planktonic bacteria are adsorbed upon particulate 

 material, including the cells of marine unicellular algae, the 

 ability of certain components of the phytoplankton to excrete 

 soluble organic products of metabolism is of further interest. 

 Such evidence as the production of extracellular peptide and 

 amide - N by algae (5) and of polysaccharide and organic acids 

 by chlamydomonads ( 1 ) supports a likelihood that relations be- 

 tween phvtoplankton cells and epiphytic bacterial populations 

 may not be incidental, and that biosynthetic capabilities of cer- 

 tain algae may qualitatively influence the local bacterial flora in 

 a selective, tliough not necessarily in a direct, manner. 



Studies of the influences of the growing plant upon the soil 

 microflora have repeatedly demonstrated that one of the most 

 characteristic effects is the preferential stimulation in the rliizo- 

 sphere of a group of bacteria dependent on amino acids (14). 

 This was ascribed on experimental evidence (7, 11) primarily to 

 the liberation of amino acids from the plant roots. Further, the 

 presence, also in the rhizosphere, of high numbers of organisms 

 for which growth factors were essential, was attributed to the 

 stimulatory eftect of the associated amino acid-requiring forms - 

 a group with a pronounced capacity for vitamin synthesis (4). 

 Little is yet known of specific reciprocal relationships of an anal- 

 ogous natiue that may integrate the acti\'ities of certain groups 

 of bacteria and other components of marine communities. It has 

 been found that, when added to \ itamin-deficient media, the 

 culture filtrates of many of those amino acid-requiring bacteria 

 that were dominant in surface waters will support growth of 

 various vitamin-requiring strains. This finding may be of signifi- 

 cance to the ecological status of tlie amino acid-requiring group 



