THERMOPHILIC SULFUR-REDUCING BACTERIA MOORELLA THERMOACETICA NADIA-3, ISOLATED FROM "NADIIA" PIT SPOIL HEAP OF CHERVONOHRAD MINING REGION

Abstract

Introduction. Thermophilic sulfate-reducing bacteria attract attention of scientists as the potential agents of purification of wastewater polluted by sulfur and its compounds, heavy metal ions and organic compounds. These bacteria oxidize different organic substrates using metals with variable valency as electron acceptors and transform them into non-toxic or less toxic forms for living organisms. However, wastewater contains high concentrations of different toxic xenobiotics, particularly, metal ions that have negative influence on living organisms. For this reason, it is important to use resistant strains of microorganisms for the purification of wastewater.
The aim of this work was to identify the thermophilic sulfur-reducing bacteria, isolated from “Nadiia” pit spoil heap of Chervonohrad mining region, and to study their properties.
Materials and Methods. Thermophilic sulfur-reducing bacteria were isolated from the samples of rock of “Nadiia” pit heap at 50 cm depth. Bacteria were cultivated in TF medium under the anaerobic conditions in  anaerostates. Cell biomass was measured turbidimetrically using the photoelectric colorimeter KFK-3 (λ = 340 nm, 3 mm cuvette). Hydrogen sulfide content was measured photoelectrocolorymetrically by the production of methylene blue. Organic acids content was measured by high performance liquid chromatography. Cr(VI), Fe(III), Мn(IV) and NO₃^– content was measured turbidimetrically.
Results. Thermophilic sulfur-reducing bacteria were isolated from the rock of “Nadiia” pit heap of Chervonohrad mining region. They were identified as Moorela thermoacetica based on the morpho-physiological and biochemical properties and on the results of phylogenetic analysis. M. thermoacetica Nadia-3 grow in the synthetic TF medium, have the shape of elongated rods, are gram-positive, endospore-forming. They form light brown colonies. Optimal growth was observed at 50–55 °C, pH 6.5–7. The bacteria utilize glucose, starch, fructose, maltose, lactose, sodium lactate, arabinose, cellulose, maltose, glycerol, fumarate, and ethanol as carbon sources. The highest sulfidogenic activity of M. thermoacetica Nadia-3 was found in media with glycerol, lactose, and glucose. M. thermoacetica Nadia-3 reduce SO₄^2-, S₂O₃^2-, Fe(III), NO₃^–, Cr(VI) compounds besides elemental sulfur. They accumulate biomass at K₂Cr₂O₇ concentrations of 0.1–1 mM. Sulfur reduction is not the main way of energy accumulation.
Conclusions. Thermophilic chromium-resistant sulfur-reducing bacteria M. thermoacetica Nadia-3, that produce hydrogen sulfide during the oxidation of different organic compounds, were isolated from the rock of “Nadiia” pit heap. They reduce Fe(III), Cr(VI), NO₃^–, SO₄^2-, S₂O₃^2-, besides elemental sulfur.