Usage of ferrum (III) and manganese (IV) ions as electron acceptors by Desulfuromonas sp. bacteria

The toxicity of metal ions to microorganisms, in particular at high concentrations, is one of the main impediments to their usage in remediation technologies. The purpose of this work is to analyze the possibility of usage by bacteria of the Desulfuromonas genus, isolated by us from Yavorivske Lake, of ferrum (III) and manganese (IV) ions at concentrations in the medium of 1,74-10,41 mM as electron acceptors of anaerobic respiration to assesss resistance of sulphur reducing bacteria strains to heavy metal compounds. Cells of Desulfuromonas acetoxidans IMV V-7384, Desulfuromonas sp. Yavor-5 and Desulfuromonas sp. Yavor-7 were cultivated for 10 days at 30 degrees C under anaerobic conditions in Kravtsov-Sorokin's medium without sulphate ions, sulphur, with cysteine as the sulphur source (0.2 g/l) and sodium lactate or citrate as the electron donor (17.86 g/l), in which were added sterile 1 M solutions of C6H5O7Fe and C4H4O4 (control) and also weights of MnO2 to their terminal concentrations 1.74, 3.47, 5.21, 6.94, 10.41 mM. Biomass was determined by the turbidimetric method. In the culture liquid the presence of Fe3+ and Mn4+ were qualitatively determined, and the content of Fe2+ in reaction with.-phenanthroline was determined quantitatively. It was established that sulphur reducing bacteria used with different intensity ferrum (III) and manganese (IV) ions as electron acceptors during the process of anaerobic respiration at concentrations of 1.74-10.41 mM C6H5O7Fe and MnO2 in the medium, which demonstrated the important role of the investigated microorganisms in reductive detoxication of natural and technogenic media from oxidized forms of transitional heavy metals. An insignificant difference in biomass accumulation during usage of 5.21-10.41 mM ferrum (III) ions and fumarate is caused by toxicity of the metal ions to cells since the high redox potential of the Fe(III)/Fe(II) pair with increase in concentrations of electron acceptors in the medium did not lead to increase in the biomass accumulation level. The greatest biomass of the bacteria accumulated on the 8-10th days in the medium with the lowest concentration of C6H5O7Fe 1.74 mM (up to 2.77 g/l), and the lowest biomass - with highest concentration - 10.41 mM (up to 2.41 g/l). After 10 days of cultivation the bacteria of all strains had fully used the ferrum (III) ions present in the medium. A biomass yield almost twice as low was revealed after manganese (IV) oxide was used by bacteria compared with its use of ferrum (III) citrate and fumarate at all studied concentrations of electron acceptors in the medium. The highest biomass of bacteria accumulated in the medium with the lowest MnO2 content - 1.74 mM (up to 1.35 g/l), and the lowest biomass in the medium with the highest content - 10.41 mM (up to 1.15 g/l). After 10 days of cultivation bacteria of all strains had not fully restored the manganese (IV) ions present in the medium. The greatest biomass compared with other strains after growth in medium with different C6H5O7Fe and MnO2 contents was accumulated by the strain Desulfuromonas sp. Yavor-7. Since sulphur reducing bacteria strains proved to be resistant to Fe3+ and Mn4+ high concentrations (up to 10. 41 mM) they can be successfully used in technologies of environmenal remediation from sulphur and heavy metal compounds.