538 



Marine Microbiology 



Fig. 3. 



medium such as the avian gut enhances the antibacterial activity, 

 while sea water is highly buffered and has an alkaline pH (8.0 

 + .5). In an attempt to determine the effect of free acrylic acid 

 upon a natural population of marine bacteria, sea water dilutions 

 of acrylic acid were added to aliquots of aseptically collected 

 samples of water from Narragansett Bay (R.I.) and counts were 

 made on the original population and after three days incubation 

 at 23 C. The original and final populations of marine bacteria at 

 the various acrylic acid concentrations as well as the original pH 

 values of the sea water of a representative trial are given in 

 Figure 3. At very small concentrations, 1-100 /'g/liter, acrylic acid 

 appeared to enhance growth. Only at concentrations above 10 

 mg/liter where the acid decreased tlie pH of the water did acrylic 

 acid suppress growth. Mean pH values of Antarctic sea water, in- 

 tact algal cells, sonic disrupted cells, and the free acrylic acid 

 fraction of Phaeocystis net hauls are also given in Figure 3. Since 

 the pH of the fresh intact cells was acidic (pH 6.05) it is very 

 possible that the microinterface between the algal cell and the 

 sea water is also acidic and antibacterial as a result of acid excre- 



