EN
The effect of a concentration of heavy metal ions (Pb2+, Cd2+, Hg2 + and Zn2+) on the process of dissimilative reduction of sulfates in medium containing active Desulphotomaculum ruminis bacteria was studied. Both tolerable and toxic concentrations of the mentioned ions were determined. According to the degree of their toxicity the following ion sequence was established: Cd2 + > Zn2+ > Hg2+ > Pb2+, but only the presence of mercury ions caused death of the bacteria.