SECTION 13 



THE IMPORTANCE OF TROPHIC BONDS IN THE 

 BACTERIAL DESTRUCTION OF ORGANIC MATTER 



P.P. Umorin'' 



In connection with the problem of purifying industrial and domestic 

 wastewaters and ascertaining the role of bacteria as a main factor in puri- 

 fying the dissolved organic matter (DOM), it is necessary to show the role 

 of organisms that feed on bacteria during the process. Unfortunately, work 

 carried out in this field and concerned with the role of the protozoa is 

 contradictory (Kryuchkoya, 1968). In the experiments of a great number of 

 authors (Butterfield, Purdy, Theriault, 1931; Phelps, 1953; Javorinsky, 

 Prokesova, 1963; Nikolyuk, 1965; Straskrabova-Prokesova, Legner, 1966; 

 Jensen, Ball, 1970), the oxygen consumption and nitrogen fixation were more 

 intensive in mixed cultures of bacteria and protozoa than in pure cultures 

 of bacteria. The results of these and other authors serve as a foundation 

 for the hypothesis first put forward by Butterfield (Butterfield, Purdy, 

 Theriault, 1931) that organisms preying upon bacteria keep the latter in a 

 state of continuous reproduction or physiological "youth" by a simple de- 

 crease of their number. This should facilitate a greater rate of decom- 

 position of organic matter. The above-mentioned authors, however, do not 

 analyze the correlation between the actual conditions of the experiment and 

 its results. In addition, the role of separate species and the quantitative 

 characteristics of the bacteria and protozoa relationships are far from 

 clear. This is especially true of the colourless flagellates. Their role 

 in the life of water bodies has almost not been studied. The aim of this 

 work is to study the rate of organic matter decomposition with bacteria and 

 protozoa in continuous cultures, maximizing the similarity to natural condi- 

 tions. 



METHODS 



All the experiments have been performed using a continuous culture de- 

 vice described previously (Umorin, 1975) with various dilution rates (D). 

 Pratt's solution served as the nutrient medium. Phenol at a concentration 

 of 25 mg/liter or glucose at a concentration of 50 mg/liter was added to 

 the solution as the only source of organic carbon. Before the experiments, 

 the reactor, 1.2 liter in volume, was filled with the nutritive medium and 

 innoculated with bacteria taken from a water-body and previously kept in a 



^The Institute of Biology of Inland Waters of the Acad. Sci. USSR. 



132 



