ecological trophic groups. At the result, complete decomposition of the aromatic compounds occurs. The ability of microorganisms to decompose xenobiotics enables solving a number of environmental problems associated with both the use of chemical pesticides and the discharge of untreated industrial wastewater.
As a result of human activity aromatic hydrocarbons enter the environment in large quantities, contaminating it. Dropping of insufficiently treated wastewater drains considerably decrease the quality of water. Quite effective biological methods of purification of contaminated environment are the usage of microorganisms. Prospective microorganisms for sewage treatment are sulfate-reducing bacteria. The purpose of the work was to investigate the ability of sulfate-reducing bacteria to use xylene and toluene as a source of carbon under different cultivation conditions. The study objects were sulfate-reducing bacteria Desulfotomaculum AR1 and Desulfovibrio desulfuricans Ya-11. The biomass of bacteria was determined turbidimetrically, the content of sulfate ion and hydrogen sulfide – photometrically in the culture fluid. The content of fumarate was determined by the method of high-performance liquid chromatography. The ability of Desulfotomaculum AR1 and D. desulfuricans Ya-11 bacteria to use toluene and xylene as the sole source of carbon and energy has been established. In the toluene environment, a better growth of bacteria was observed. A comparison was made between the efficiency of the reduction of sulfate ions and the growth of bacteria in the control medium and the medium with aromatic compounds. The efficiency of sulfate ions reduction was sufficiently high in the control medium, whereas in the toluene/xylene media the efficiency of sulfate utilization and hydrogen sulfide accumulation was lower compared to the control parameters. The growth of Desulfotomaculum AR1 and D. desulfuricans Ya-11 sulfate-reducing bacteria was investigated in xylene and toluene media in the presence/absence of fumarate. According to the results of the studies, the best growth of the tested bacteria was observed in the medium with aromatic compounds in the presence of fumarate and sulfate ion. Efficiency of use of fumarate in the medium with toluene with bacteria Desulfotomaculum AR1 was more than 90 %. Fumarate can be used by sulfate-reducing bacteria as a source of carbon, donor and acceptor of electrons. Fumarate is most likely to inhibit sulfate reduction in Desulfotomaculum AR1 and D. desulfuricans Ya-11 bacteria, as indicated by studies showing that sulfate reduction efficiency in lactate, fumarate, and sulfate ion media was half that of control. Sulfate-reducing bacteria are capable to anaerobically degrade aromatic hydrocarbons in the presence of sulfate ions as terminal electron acceptors. The ability of sulfate-reducing bacteria Desulfotomaculum AR1 and D. desulfuricans Ya-11 to use the aromatics of the BTEХ – toluene, xylene and sulfate-ions, makes them promising at the biological purification step of contaminated wastewater from these pollutants.
The aim of this work was to study the patterns of utilization of sulfate and nitrate ions by bacteria Desulfomicrobium sp. CrR3 and Desulfovibrio desulfuricans Ya-11 under different cultivation conditions. Chromium-resistant sulfate-reducing bacteria Desulfomicrobium sp. CrR3 and D. desulfuricans Ya-11 were used. Bacteria were grown in Posgate C medium at 30°C in 25 ml test tubes under anaerobic conditions. To test the ability of bacteria Desulfomicrobium sp. CrR3 and D. desulfuricans Ya-11 to use various substances and ions as electron acceptors, they were incubated in potassium phosphate buffer (10 mM, pH 7) with sulfate, nitrate and nitrite ions in concentrations of 1, 5 and 10 mM. At various concentrations of sulfate ions (1, 5 and 10 mM), biomass of bacteria Desulfomicrobium sp. CrR3 and D. desulfuricans Ya-11 increased with the increase of concentration of electron acceptor, the maximum biomass was equal to 3.65 and 3.05 g/l at 10 mM of sulfate ions, respectively. With the increase of concentration of nitrate ions to 5 mM the biomass increased by 70% compared to the biomass of bacteria grown in the medium with nitrate ions at the concentration 1 mM. The maximal biomass was determined in the presence of nitrate ions at a concentration of 10 mM – 3.78 and 3.15 g/l for bacteria Desulfomicrobium sp. CrR3 and D. desulfuricans Ya-11, respectively. It is found, as a result of incubation of bacteria Desulfomicrobium sp. CrR3 and D. desulfuricans Ya-11, that by introducing sulfate ions at a concentration of 5 mM bacteria Desulfomicrobium sp. CrR3 used 98%, while D. desulfuricans Ya-11 used only 86%, and under these conditions hydrogen sulfide has been detected in the incubation mixture at the concentration of 0.8–1.0 mM. In the presence of 10 mM of sulfate ions efficiency of electron acceptors utilization was equal to 85–95% for both strains. Bacteria Desulfomicrobium sp. CrR3 intensively used nitrate ions, the efficiency of electron acceptor utilization at 10 mM was equal to 92.8%, while for D. desulfuricans Ya-11 the usage percent amounted to 73% only, and nitrite ions were not observed after three days of incubation. It is established that bacteria Desulfomicrobium sp. CrR3 and D. desulfuricans Ya-11 are capable to use sulfate and nitrate ions as electron acceptors in the process of the disimilatory sulfate and nitratre reduction. As a result of the study of patterns of nitrate utilization by Desulfomicrobium sp. CrR3 and D. desulfuricans Ya-11 it is found that bacteria use nitrate as a nitrogen source for biosynthetic processes, and as electron acceptors. Under these conditions nitrates are reduced to nitrites, and then they are turned to ammonium.
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