Sulfidogenic and metal reducing activities of Desulfuromonas genus bacteria under the influence of copper chloride

Abstract

The selection of strains isolated from technogenically altered ecotopes and resistant to contamination, capable of metabolizing a wide range of pollutants is a task highly relevant for creation of new methods for environmental purification. Sulphur-reducing bacteria of the Desulfuromonas genus carry out dissimilatory reduction not only of S0 but also oxidized forms of metals. Intensity of anaerobic respiration of microorganisms in polluted environments is determined by level of their adaptation to stress factors, in particular, copper (II) compounds. The aim of this work was to investigate the influence of copper (II) chloride on H2S production by Desulfuromonas sp. strains isolated by us from Yavorivske Lake, to determine the efficiency of Cu2+ precipitation by hydrogen sulfide, to analyse the possibility of usage by bacteria of CuCl2 as an electron acceptor of anaerobic respiration and to study the influence of Cu2+ on usage by these microorganisms of ferric (III) citrate, potassium dichromate or manganese (IV) oxide as electron acceptors. Bacteria were grown under anaerobic conditions in Kravtsov-Sorokin medium. To study the influence of Cu2+ on production by bacteria of H2S, their cells were incubated with CuCl2 (0.5–4.0 mM), washed and cultivated in a medium with S0. To determine the level of Cu2+ binding by H2S, produced by bacteria, cells were grown in a medium with CuCl2 (0.5–4.0 mM) and S0. To investigate the ability of bacteria to use copper (II) ions as electron acceptors, they were cultivated in a medium with CuCl2 (1.74–10.41 mM). To study the influence of Cu2+ on usage by bacteria of metal compounds as electron acceptors, their cells were incubated with CuCl2 (0.5–4.0 mM), washed and cultivated in media with C6H5O7Fe, K2Cr2O7 or MnO2 (1.74–10.41 mM). Biomass was determined by the turbidimetric method. In the cultural liquid the content of H2S was determined quantitatively by the spectrophotometric method, qualitatively – presence of Cu2+. Content of CuS in the growth medium was determined by weight method. Desulfuromonas sp. bacteria was revealed to be resistant to 2.0–2.5 mM copper (II) ions. Under the influence of 3.0–4.0 mM CuCl2 in the incubation mixture, sulfidogenic activity of bacteria decreased more than twice. The efficiency of Cu2+ binding in form of CuS by H2S produced by bacteria reached 97.3–100.0% at presence in the medium with S0 of up to 1.5 mM CuCl2. Bacteria used CuCl2 (1.74–10.41 mM) as an electron acceptor in the process of anaerobic respiration. The addition of 2.5–3.0 mM CuCl2 to the incubation mixture caused inhibition of metal reducing activity of cells, growth of all strains in media with 1.74–10.41 mM ferric (III) citrate, potassium dichromate or manganese (IV) oxide as electron acceptors decreased by 2.6 times. Almost complete precipitation up to 1.5 mM copper (II) ions in form of CuS by H2S produced by bacteria and ability to reduce up to 10.41 mM CuCl2, C6H5O7Fe, K2Cr2O7 or MnO2 in the process of anaerobic respiration indicates a high adaptation of the bacteria strains investigated by us to stress factors, in particular, the influence of CuCl2. We have proved the possibility of using Desulfuromonas sp. in biotechnologies for purification of environments with complex contamination from copper (II) compounds.

Keywords

• sulphur-reducing bacteria; hydrogen sulfide; copper; heavy metals.