Reduction of sulfate, nitrate and nitrite ions by Desulfovibrio sp. under the influence of ferrum (III) citrate

Abstract

The influence of ferrum (III) citrate added to the cultivation medium, on the reduction of sulfate, nitrate, and nitrite ions by sulfate-reducing bacteria Desulfovibrio desulfuricans IMV K-6, Desulfovibrio sp. Yav-6, and Desulfovibrio sp. Yav-8 isolated from Yavorivske Lake was studied. It was established that ferrum (III) citrate inhibits the biomass accumulation, SO₄^2- reduction, and H₂S production by the bacteria after addition of 1.74–3.47 mM Na₂SO₄×10 H₂O and 1.74–10.41 mM FeC₆H₅O₇ to the medium, in comparison with the growth and level of the reduction of sulfate ions by bacteria in the medium supplemented with only Na₂SO₄×10 H₂O. At conditions of the bacteria cultivation in the presence of an equimolar amount (3.47 mM) of Na₂SO₄×10 H₂O and FeC₆H₅O₇, they reduced 2.5−2.7 times more Fe(ІІІ) than SO₄^2- with Fe²⁺ production at a concentration 2.4−2.7 times greater than H₂S. FeC₆H₅O₇ inhibited growth, NO₃^- or NO₂^- reduction and NH₄⁺ production by the bacteria in the presence of 1.74−3.47 mM NaNO₃ or NaNO₂ and 1.74−10.41 mM FeC₆H₅O₇ in the medium, compared to the growth and level of nitrate or nitrite ions reduction in the medium with only NaNO₃ or NaNO₂. In the medium with the same initial content of 3.47 mM NaNO₃ and 3.47 mM FeC₆H₅O₇, the bacteria reduced 1.4 times more NO₃^- than Fe(ІІІ), with NH₄⁺ production at concentration 1.1 times higher than that of Fe²⁺. In the medium with 3.47 mM NaNO₂ and 3.47 mM FeC₆H₅O₇, the cells reduced 1.4−1.6 times more Fe(ІІІ) than NO₂^-, with Fe²⁺ production at concentra­tion 1.5−1.6 times higher than NH₄⁺. Ferrum (III) citrate had more inhibitory effect on the dissimilatory reduction of sulfate by the bacteria than of nitrate and nitrite ions, since the SO₄^2- reduction by the bacteria at its presence in the medium decreased 2.0−4.7 times. The reduction of NO₃^- and NO₂^- decreased only 1.3−1.9 and 1.7−3.1 times, respectively, as compared with their reduction in the media with only Na₂SO₄×10 H₂O, NaNO₃ or NaNO₂. Despite the fact that the reduction by cells of 1.74−10.41 mM Fe(III) in the media with Na₂SO₄×10 H₂O, NaNO₃ or NaNO₂ decreased 1.1−2.1, 1.6−2.7 and 1.1−2.5 times, respectively, compared with its reduction in the medium with only FeC₆H₅O₇. The investigated strains of bacteria were resistant to high concentrations of ferrum (III) citrate and, therefore, can be applied in the technologies of complex environment purification from pollution with ferrum, sulfur, and nitrogen compounds. Keywords: Desulfovibrio, ferrum, sulfates, nitrates, nitrites