| Summary: | The ability of a number of microorganisms isolated from highly magnetic soil of the city Mednogorsk to oxidize Fe (II) under conditions of periodic cultivation in a liquid medium was studied. Among the studied microorganisms, two microbial isolates with maximum growth characteristics and iron-oxidizing activity were selected and identified: <i>Bacillus megaterium</i> 69.3 and <i>B. megaterium</i> 69.5. Individual levels of metal resistance of the isolates were determined: maximum tolerated concentration (MTC) for Fe (II) of the isolates <i>B. megaterium</i> 69.3 and <i>B. megaterium</i> 69.5 was 1200 mg L<sup>−1</sup>, minimum inhibitory concentration (MIC) was 1800 mg L<sup>−1</sup>. Both microbial isolates actively oxidized Fe (II) by reducing its high concentration in the medium (1.19 g L<sup>−1</sup>) by 33 and 39% during 14 days of culturing. Total increase in the biomass of <i>B. megaterium</i> 69.3 and <i>B. megaterium</i> 69.5 after 14 days of culturing was 15.3 and 14.7 g L<sup>−1</sup>; the active parts of the biomass increased 8.7- and 6.9-fold compared to the inoculum dose, respectively. These microbial isolates could be used in future in the biotechnological process of water purification with increased/high levels of Fe (II).
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