706 



Marine Microbioloiiy 



plankton and bacteria, 1.44 per cent and 1.04 per cent of the 

 total number of food cells. This means that the cells of both food 

 components are ingested simultaneously, but at unequal amounts. 

 Taking into account the natural concentration of cells of bac- 

 teria and planktonic algae in the habitat of calanipeds in the Sea 

 of Azov as well as the composition of the cells, their size and 

 species and the rate of consumption of food cells, the figures show 



0.7H 



o 



^ 0.6H 



2 0.5- 



UJ 



S 04- 



■z. 0.3- 

 o 



2 O.2. 



I- 



u: o.H 



-1 — 



30 



—I— 

 40 



60 



10 20 30 40 50 



CONCENTRATION OF FOOD CELLS {phytoplankton) 

 IN Thous/ml 



Fig. 2. Dependence of the filti'ation rate on food concentration. 



that the weight of bacteria consumed is 1/5 that of the weight of 

 phytoplankton (Table 4). 



Using the radioactive tracer, C^^, it has been proved that 

 bacteria are not only ingested by the representatives of plankton, 

 but are also assimilated. The experiment was designed to obtain 

 bacterial cells bearing the isotope tracer which could serve as 

 food for plankters, and after the bacteria were ingested, to find 

 the tracer in the body of the filtrator. 



It is comparatively easy to obtain bacteria which bear the 

 tracer by adding a radioactive element to a compound in an 

 artificial nutritive medium in which microorganisms are culti- 

 vated. However, bacteria cultivated in artificial nutritive media 



