The influence of different substances upon microorganisms may be deter- 

 mined using both pure and mixed cultures. One may also study the effect on 

 bacteria of various substances, for example, heavy metals, antibiotics, 

 antiseptics, pesticides, or toxic solutions of waste waters. Additionally, 

 the effect of temperature, pH, redox conditions and the like may be consid- 

 ered. In all the cases, it is necessary to take into account the presence 

 in the test water of other carbonate material. While it does not influence 

 the absolute value of CO2 assimilation, it can effect the values of radio- 

 active uptake. 



When studying the influence of toxicants on microorganisms, a nutrient 

 medium is prepared for bacteria. Weak solutions of meat-peptone broth may 

 be used. After sterilization and adjusting the pH value circum neutral 

 conditions, the medium is inoculated with a young culture distributed into a 

 series of 5-10 ml test tubes. The test is added to each at a required con- 

 centration, along with 0.1 or 1 ml of the labeled carbonate with an activity 

 of 0.5-1.0 x 106 imp/min. The test tubes are then plugged with rubber stop- 

 pers and placed in an incubator for one day after which the samples are 

 fixed with formalin and filtered through a membrane filter which retains the 

 bacteria. After treatment with weak hydrochloric acid (1 percent solution) 

 the filters are dried and the radioactivity is measured. The effect of 

 various concentrations of the tested substance on bacteria is indicated by 

 the radioactivity. The samples without the test substance serve as con- 

 trols. Their radioactivity is assumed to be 100 percent. The results of 

 one of such experiment on the action of silver ions are shown in Figure 4. 

 Silver concentrations of 10~8 - 10"? M have no effect on bacteria. The in- 

 fluence of these ions was detected beginning with the concentration 10~6 M, 

 with complete inhibition of metabolism occurring at a concentration of 

 10" 5 M. 



This scheme may be used for determination of the toxicity of waste 

 waters. When the presence thermostable substances is expected, the samples 

 may be heated to 80 C for 10 min. to kill microflora, and then be added 

 into test tubes with indicator organisms. Alternatively, one may eliminate 

 preliminary heating and consider the control. 



Determination of the Reserve and Rate of Consumption of Organic Substances 

 According to the Method of Right and Hobbie 



The living activity of microorganims may be estimated by the intensity 

 of consumption of labeled organic compounds (Right and Hobbie, 1965). The 

 method is based on the regularities of enzyme reactions. It allows the 

 determination of the speed of circulation of separate organic substances 

 and their reserves. Labeled glucose or acetate are most frequently used 

 for this purpose. 



The water to be tested is poured into 9 bottles of 30-50 ml each which 

 are arranged in two parallel rows, four in each, with one remaining for 

 control of the purity of the labeled substance. To the first two bottles 

 are added 0.05 ml of the solution, to the second two bottles, twice the 

 greater amount and so on. To the 9th bottle is added a fixative (Lugol's 

 solution or formalin) and 0.1 ml of the solution of labeled substance. 



69 



