weights in mg/liter. The latter were calculated from their biovolume; 

 specific gravity of the wet biomass was accepted as an equal unit and the 

 dry weight - 15% of the biomass. The mean volume of bacteria developing on 

 the medium with phenol was 1 y 3 , and on the medium with glucose 0.5 y 3 ; in 

 this case, 1 mg of dry weight of bacteria per liter is equivalent to 7.5 

 million and 15 million cells per milliliter, respectively. With the mean 

 volume of P_. jaculans 25 y 3 , 1 mg of dry weight per liter corresponds to 

 the number 300 thousand cells per ml of this flagellate. The dry weight of 

 one infusorian P_. caudatum was taken from G.G. Vinberg's work (Vinberg, 

 1949), 0.08 x 10" 3 mg. Then their dry weight of 1 mg/liter is equivalent 

 to the number 12.5 cells/ml. Concurrently with a calculation of the number 

 of organisms, the phenol concentration was determined by pyramidone method 

 (Lurie, Rybnikova, 1966), and that of glucose by a reagent with phenol 

 (Bikbulatov, Skopintsev, 1974). 



RESULTS 



In all the experimentally conditions, a steady component value was esta- 

 blished in the reactor, according to the type of damped oscillations in ex- 

 periments 2, 4, and 6, and aperiodically in the remaining ones. On the com- 

 plete Pratt media, the concentration of the organic matter in the reactor 

 was established at a higher level in the experiments with protozoa than 

 without them. This indicates that when mineral nutrients are provided and 

 the growth rate of bacteria is limited only by the concentration of organic 

 matter, the bacteria alone decompose it faster than in the mixed cultures 

 with protozoa. Since the number of bacteria in the presence of protozoa was 

 significantly lower than without them, the decrease in the rate of decom- 

 position of organic matter may be explained by the decrease in the number 

 of bacteria due to predation by protozoa. Nevertheless, in the experiments 

 with nitrogen deficiency, destruction of organic matter proceeded faster in 

 the presence of protozoa, in spite of the decrease in the number of bac- 

 teria; i.e., one and the same factor, protozoa, may either accelerate or 

 slow down destruction of organic matter depending upon the condition. 



TABLE 1. VALUES OF THE COMPONENTS IN MG/LITER (DRY WEIGHT) 

 AT THE STEADY STATE (AVERAGE THREE REPETITIONS). 



134 



