SULFATE -REDUCING BACTERIA RESISTANT TO INCREASED LEVELS OF HEXAVALENT CHROMIUM

Abstract

The aim of this work was to study the morpho-physiological and biochemical properties of chromium-resistant sulfate-reducing bacteria and to investigate the nature of electron donors and their acceptors. Methods. Bacteria were cultivated in Postgate B and Postgate C media at temperature 30 °C in 25 ml tubes under the anaerobic conditions. Biomass was determined turbidimetrically using the photoelectrocolorimeter CPK-3 The concentration of Cr (VI) was determined spectrophotometrically by the diphenylcarbazide method. Chromazurol S was used for Cr (III) determination. The sulphates content was determined turbidimetrically after their precipitation by barium chloride. Results. Bacterial cells are oval or rod-shaped. Derived sulfate-reducing bacteria hold incomplete oxidation of organic compounds with acetate formation and do not form spores, gramnegative, mesophillous obligate anaerobes. The optimum temperature for growth is 27–35 °C, pH=7. As a final electron acceptor sulfate-reducing bacteria use sulfate. Bacteria use elemental sulfur, fumarate, Cr (VI), Fe (III), nitrate as a terminal electron acceptor under absence of sulfate in the environment. In presence of sulfate in culture medium all cultures as a source of carbon, used lactate, fumarate, pyruvate, succinate, malate, fructose, glucose, citrate. Acetate, ethanol, butanol, propionate, glycerol did not provide their growth. The effect of different concentrations of chromate on the growth of sulfate-reducing bacteria have been investigated. There were shown the patterns of use of chromate by bacteria, and reduction highly toxic Cr (VI) to less toxic Cr (III). Conclusions. Isolated bacteria, were identified as Desulfomicrobium sp. These sulfate-reducing bacteria, in our opinion, can be used for treatment of water environment from sulfates, nitrates and salts of heavy metals and especially hexavalent chromium.